The document summarizes recent research on new electro-optic properties of polysiloxane liquid crystal polymers. A series of polysiloxane-based side-chain liquid crystal polymers were prepared with systematic variation in spacer length between the mesogenic units and the polymer backbone. Electro-optic measurements showed that threshold voltage decreased with increasing spacer length. This was attributed to changes in intrinsic curvature elasticity rather than orientational order. Threshold voltage also decreased with increasing temperature and orientational order parameter. The results were consistent with existing models of curvature deformation in liquid crystals and provided insight into the effects of constraints from coupling mesogenic units to the polymer backbone.
In this paper, the analysis of optically responsive microfibers with uniaxially ordered liquid crystal (LC) molecules at their cores is discussed. LC microfibers were electrospun from a solution of poly(vinyl pyrrolidone) (PVP) and N-(4-methoxybenzylidene)-4$-butylaniline (MBBA) using absolute alcohol as a solvent. Two parallel copper (Cu) collectors were used to obtain ordered fibers. The microfibers with oriented LC molecules were well fabricated at a voltage of 5 kV. A thermal-optical analysis revealed that the fibers were responsive to temperature. The rise of temperature from nematic to isotropic phase of LC decreased the LC intensity under a polarized optical microscope (POM).
Electro catalytic performance of pt-supported poly (o-phenylenediamine) micro...sunitha81
Poly (o-phenylenediamine) (PoPD) microrods were obtained by interfacial
polymerization using ferric chloride as oxidant and without any template or
functional dopant. Pt/PoPD nanocatalysts were prepared by the reduction of chloroplatinic
acid with sodium borohydride, and the composite catalysts formed were
characterized by X-ray diffraction and electrochemical methods. The nanocomposite
of Pt/PoPD microrods has been explored for their electro-catalytic performance
towards oxidation of methanol. The electro-catalytic activity of Pt/PoPD was
found to be much higher (current density 1.96 mA/cm2 at 0.70 V) in comparison to
Pt/Vulcan electrodes (the current density values of 1.56 mA/cm2 at 0.71 V) which
may be attributed to the microrod morphology of PoPD that facilitate the effective
dispersion of Pt particles and easier access of methanol towards the catalytic sites.
In this paper, the analysis of optically responsive microfibers with uniaxially ordered liquid crystal (LC) molecules at their cores is discussed. LC microfibers were electrospun from a solution of poly(vinyl pyrrolidone) (PVP) and N-(4-methoxybenzylidene)-4$-butylaniline (MBBA) using absolute alcohol as a solvent. Two parallel copper (Cu) collectors were used to obtain ordered fibers. The microfibers with oriented LC molecules were well fabricated at a voltage of 5 kV. A thermal-optical analysis revealed that the fibers were responsive to temperature. The rise of temperature from nematic to isotropic phase of LC decreased the LC intensity under a polarized optical microscope (POM).
Electro catalytic performance of pt-supported poly (o-phenylenediamine) micro...sunitha81
Poly (o-phenylenediamine) (PoPD) microrods were obtained by interfacial
polymerization using ferric chloride as oxidant and without any template or
functional dopant. Pt/PoPD nanocatalysts were prepared by the reduction of chloroplatinic
acid with sodium borohydride, and the composite catalysts formed were
characterized by X-ray diffraction and electrochemical methods. The nanocomposite
of Pt/PoPD microrods has been explored for their electro-catalytic performance
towards oxidation of methanol. The electro-catalytic activity of Pt/PoPD was
found to be much higher (current density 1.96 mA/cm2 at 0.70 V) in comparison to
Pt/Vulcan electrodes (the current density values of 1.56 mA/cm2 at 0.71 V) which
may be attributed to the microrod morphology of PoPD that facilitate the effective
dispersion of Pt particles and easier access of methanol towards the catalytic sites.
Design of fragment screening libraries (Feb 2010 version)Peter Kenny
I have lectured on design of fragment screening libraries a number of times and, to be honest, my material is getting a bit dated. This presentation is from Feb 2010 when I was visiting CSIRO and the photo in the title slide was taken in Tierra del Fuego.
Growth and Characterization of Barium doped Potassium Hydrogen Phthalate Sing...IJERA Editor
The Non Linear Optical materials have acquired new significance with the advent of a large number of devices
utilizing solid state Laser sources. Potassium Hydrogen Phthalate one of the Non Linear Optical material having
superior non linear optical properties has been exploited for variety of application. In the present work, KHP
single crystals were grown by slow evaporation technique with Barium metal ion as a dopant. The grown
crystals were subjected to powder XRD analysis and the result shows that the Ba2+ ions does not alter the crystal
structure, but it enter into the crystal lattice of pure KHP. The optical transparency of the grown crystal was
studied by UV-Visible spectroscopy, the molecular structure was confirmed by FTIR analysis and its thermal
stability by TG/DTA analysis. The improved SHG efficiency of barium doped Potassium Hydrogen Phthalate
crystal could enhance the nonlinearity behaviour. In addition to this, the electrical parameter such as dielectric
constant was studied in detail.
Growth, structural, mechanical and dielectric studies of undoped and urea dop...Editor IJCATR
Undoped and urea doped L-alaninium maleate crystals were grown by solution method with slow evaporation technique.
Solubility studies were carried out for the grown crystals and it is found that solubility increases with temperature for both the samples.
XRD studies were performed to find the crystal structure of the samples. NLO activity of the grown crystals was studied using a
Nd:YAG laser and SHG efficiency was found for both the samples. Microhardness studies were performed to understand the
mechanical strength of the samples. Measurements of values of dielectric constant and dielectric loss were carried out and the
electrical processes that are taking place in the samples are discussed
Electrochemical Behavior of L-Tyrosine at Poly (Dicyclomine Hydrochloride) Fi...paperpublications3
Abstract: An electrochemical method for the determination of L-Tyrosine (LTY) using a dicyclomine hydrochloride (DICY) polymer film modified carbon paste electrode. The surface morphology of poly (DICY) modified carbon paste electrode was characterized by SEM. The modified electrode showed excellent electro catalytic activity towards the oxidation of LTY in 0.1 M phosphate buffer solution of pH 6.5. The effect of pH, concentration and scan rate were studied at the bare carbon paste electrode and poly (DICY) modified carbon paste electrode were investigated. Increase of LTY concentration shows linear increase in oxidation peak current. The linear relationship was obtained between the anodic peak current (Ipa) and concentration LTY in range 2×10-5 M to 1×10-3 M with correlation coefficient of 0.9984. The low detection limit (LOD) and low quantification limit (LOQ) of LTY were detected. The cyclic voltammetric studies indicated that the oxidation of LTY at the modified electrode surface was irreversible; adsorption controlled and undergoes a one electron transfer process at the poly (DICY) film modified carbon paste electrode. The modified electrode showed high sensitivity, detection limit, high reproducibility, easy preparation and regeneration of the electrode surface.
M.Sc. Chemical Engineering Thesis Defense (Omer Farooqi)Omer Farooqi
This is the presentation for my M.Sc. research thesis. I worked on a novel electrode preparation method to carry out voltammetry in order to detect heavy metals in water.
Introduction
working principle
fragmentation process
general rules for fragmentation
general modes of fragmentation
metastable ions
isotopic peaks
applications
A series of siloxane based side chain liquid crystal polymers have been prepared with asystematic variation in spacer length. Nematic liquid crystal polymers possess large optical nonlinearities owing to their large refractive index anisotropy coupled with the collective molecular reorientation. All the polymer exhibited a smectic phase, for which the Nematic -isotropic transition temperature increased as the spacer length increased. Electro-optic measurements are used to evaluate the threshold voltages for this series of polymers. It is found that with increasing spacer length (n) of polymer the threshold voltage is lowered and that the variation of the threshold voltage arises from changes to the intrinsic curvature elasticity rather than to differences in orientational order. A simple model is used to indicate the origion of the effects observed which appear to arise from the constraints offered by the coupling of the mesogenic units to the polymer backbone.
Design of fragment screening libraries (Feb 2010 version)Peter Kenny
I have lectured on design of fragment screening libraries a number of times and, to be honest, my material is getting a bit dated. This presentation is from Feb 2010 when I was visiting CSIRO and the photo in the title slide was taken in Tierra del Fuego.
Growth and Characterization of Barium doped Potassium Hydrogen Phthalate Sing...IJERA Editor
The Non Linear Optical materials have acquired new significance with the advent of a large number of devices
utilizing solid state Laser sources. Potassium Hydrogen Phthalate one of the Non Linear Optical material having
superior non linear optical properties has been exploited for variety of application. In the present work, KHP
single crystals were grown by slow evaporation technique with Barium metal ion as a dopant. The grown
crystals were subjected to powder XRD analysis and the result shows that the Ba2+ ions does not alter the crystal
structure, but it enter into the crystal lattice of pure KHP. The optical transparency of the grown crystal was
studied by UV-Visible spectroscopy, the molecular structure was confirmed by FTIR analysis and its thermal
stability by TG/DTA analysis. The improved SHG efficiency of barium doped Potassium Hydrogen Phthalate
crystal could enhance the nonlinearity behaviour. In addition to this, the electrical parameter such as dielectric
constant was studied in detail.
Growth, structural, mechanical and dielectric studies of undoped and urea dop...Editor IJCATR
Undoped and urea doped L-alaninium maleate crystals were grown by solution method with slow evaporation technique.
Solubility studies were carried out for the grown crystals and it is found that solubility increases with temperature for both the samples.
XRD studies were performed to find the crystal structure of the samples. NLO activity of the grown crystals was studied using a
Nd:YAG laser and SHG efficiency was found for both the samples. Microhardness studies were performed to understand the
mechanical strength of the samples. Measurements of values of dielectric constant and dielectric loss were carried out and the
electrical processes that are taking place in the samples are discussed
Electrochemical Behavior of L-Tyrosine at Poly (Dicyclomine Hydrochloride) Fi...paperpublications3
Abstract: An electrochemical method for the determination of L-Tyrosine (LTY) using a dicyclomine hydrochloride (DICY) polymer film modified carbon paste electrode. The surface morphology of poly (DICY) modified carbon paste electrode was characterized by SEM. The modified electrode showed excellent electro catalytic activity towards the oxidation of LTY in 0.1 M phosphate buffer solution of pH 6.5. The effect of pH, concentration and scan rate were studied at the bare carbon paste electrode and poly (DICY) modified carbon paste electrode were investigated. Increase of LTY concentration shows linear increase in oxidation peak current. The linear relationship was obtained between the anodic peak current (Ipa) and concentration LTY in range 2×10-5 M to 1×10-3 M with correlation coefficient of 0.9984. The low detection limit (LOD) and low quantification limit (LOQ) of LTY were detected. The cyclic voltammetric studies indicated that the oxidation of LTY at the modified electrode surface was irreversible; adsorption controlled and undergoes a one electron transfer process at the poly (DICY) film modified carbon paste electrode. The modified electrode showed high sensitivity, detection limit, high reproducibility, easy preparation and regeneration of the electrode surface.
M.Sc. Chemical Engineering Thesis Defense (Omer Farooqi)Omer Farooqi
This is the presentation for my M.Sc. research thesis. I worked on a novel electrode preparation method to carry out voltammetry in order to detect heavy metals in water.
Introduction
working principle
fragmentation process
general rules for fragmentation
general modes of fragmentation
metastable ions
isotopic peaks
applications
A series of siloxane based side chain liquid crystal polymers have been prepared with asystematic variation in spacer length. Nematic liquid crystal polymers possess large optical nonlinearities owing to their large refractive index anisotropy coupled with the collective molecular reorientation. All the polymer exhibited a smectic phase, for which the Nematic -isotropic transition temperature increased as the spacer length increased. Electro-optic measurements are used to evaluate the threshold voltages for this series of polymers. It is found that with increasing spacer length (n) of polymer the threshold voltage is lowered and that the variation of the threshold voltage arises from changes to the intrinsic curvature elasticity rather than to differences in orientational order. A simple model is used to indicate the origion of the effects observed which appear to arise from the constraints offered by the coupling of the mesogenic units to the polymer backbone.
Nanobiosensors can be built via functionalization of atomic force microscopy (AFM) tips with
biomolecules capable of interacting with the analyte on a substrate, and the detection being
performed by measuring the force between the immobilized biomolecule and the analyte.
The optimization of such sensors may require multiple experiments to determine suitable
experimental conditions for the immobilization and detection. In this study we employ molecular
modeling techniques to assist in the design of nanobiosensors to detect herbicides. As a proof
of principle, the properties of acetyl co-enzyme A carboxylase (ACC) were obtained with
molecular dynamics simulations, from which the dimeric form in an aqueous solution was
found to be more suitable for immobilization owing to a smaller structural fluctuation than
the monomeric form. Upon solving the nonlinear Poisson–Boltzmann equation using a
finite-difference procedure, we found that the active sites of ACC exhibited a positive surface
potential while the remainder of the ACC surface was negatively charged. Therefore, optimized
biosensors should be prepared with electrostatic adsorption of ACC onto an AFM tip
functionalized with positively charged groups, leaving the active sites exposed to the analyte.
The preferential orientation for the herbicides diclofop and atrazine with the ACC active site
was determined by molecular docking calculations which displayed an inhibition coefficient
of 0.168 mM for diclofop, and 44.11 mM for atrazine. This binding selectivity for the herbicide
family of diclofop was confirmed by semiempirical PM6 quantum chemical calculations which
revealed that ACC interacts more strongly with the herbicide diclofop than with atrazine,
showing binding energies of 119.04 and +8.40 kcal mol1, respectively.
Role of αc–relaxation in high-temperature polymer deformation.
Proceedings of the American Society for Composites 2009-Twenty-Fourth Technical ConferenceWith the Canadian Association for Composite Structures and Materials (Joint Canadian-American International Conference), September 15-17, Newark, DE
Impact of Gamma Irradiation on Structural and Dielectric Properties of CuI-PV...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
Characterization of Electrospun Nafion-Poly Acrylic Acid Membranes, Breakthro...drboon
Problem statement: In this paper we focus on discussing the mechanical properties of electrospun Nafion-PAA membranes. Approach: We prepared solutions of varying composition ratios of Nafion and PAA in order to create the membranes using the electrospinning process. After the confection of the membranes they were studied using SEM Microscopy and various methods of mechanical properties determination. Results: Results have determined that the 80%Nafion/20%PAA heat treated post compacted membranes have the best water uptake. Conclusion: The membranes produced are superior to those commercially produced in regards to water uptake, especially those of Order 1.
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Key Trends Shaping the Future of Infrastructure.pdfCheryl Hung
Keynote at DIGIT West Expo, Glasgow on 29 May 2024.
Cheryl Hung, ochery.com
Sr Director, Infrastructure Ecosystem, Arm.
The key trends across hardware, cloud and open-source; exploring how these areas are likely to mature and develop over the short and long-term, and then considering how organisations can position themselves to adapt and thrive.
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Encryption in Microsoft 365 - ExpertsLive Netherlands 2024Albert Hoitingh
In this session I delve into the encryption technology used in Microsoft 365 and Microsoft Purview. Including the concepts of Customer Key and Double Key Encryption.
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
From Siloed Products to Connected Ecosystem: Building a Sustainable and Scala...
A04 06 0108
1. International Journal of Engineering Inventions
e-ISSN: 2278-7461, p-ISSN: 2319-6491
Volume 4, Issue 6 (November 2014) PP: 01-08
www.ijeijournal.com Page | 1
New Electro-Optic Properties of Polysiloxane Liquid Crystals
Khalid Al.Ammar1
, Sura Al.Asadi
Departrat of Physics ,– College of Education for pure sciences–University of Babylon
Abstract: This review focuses on recent developments in the chemistry of side chain liquid crystal polymers. It
concentrates on current trends in synthetic methods and novel,well defined structures, supramolecular arrangements,
properties, and applications. A series of siloxane based side chain liquid crystal polymers have been prepared with
asystematic variation in spacer length.Nematic liquid crystal polymers possess large optical nonlinearities owing to
their large refractive index anisotropy coupled with the collective molecular reorientation. All the polymer exhibited a
smectic phase, for which the Nematic-isotropic transition temperature increased as the spacer length increased.
Electro-optic measurements are used to evaluate the threshold voltages for this series of polymers. It is found that with
increasing spacer length (n) of polymer the threshold voltage is lowered and that the variation of the threshold voltage
arises from changes to the intrinsic curvature elasticity rather than to differences in orientational order. A simple
model is used to indicate the origion of the effects observed which appear to arise from the constraints offered by the
coupling of the mesogenic units to the polymer backbone.
Keywords: The spacer length polysiloxane, liquid crystal polymers, electro – optic properties.
I. Introduction
Over thirty years ago the work of Finkelmann and Ringsdorf [1,2] gave important momentum to synthesis of
side chain liquid crystal polymers (SCLCPs), materials which combine the anisotropy of liquid crystalline mesogens
with the mechanical properties of polymers. Side chain liquid crystal polymers are a composite from of macromolecule
built up from three basic types of molecular unit. These are the polymer backbone, the mesogenic units, and the
coupling chains which link the mesogenic unit to the polymer chain. A large number of sidechain polymers in which the
nature of these three components and their interconnection are varied have been synthesised and studied [2,3]. They are
classified as main-chain LCP where mesogenic groups are part of the polymer backbone. Another approach was to link
the rigid group to a polymer backbone as side chains (side-chain LCP)[4].it was necessary to give the mesogens some
more freedom of movement as they were already very restricted while being part of a polymer. This could be achieved
by increasing the spacer length between the mesogens. although the level of coupling in either case is relatively small.
Studied involving cross-linked systems[4] and fibres [5] have shown that there is a regular alternation in the sign of the
coupling for a particular polyacrylate and polysiloxane based systems as the length of the coupling chain is increased.
This realignment, which takes place on a time scale order of magnitude faster for side – chain polymer in comparison
with the main – chain system, allows the optical properties of such materials . In particular we centre our attention on
the influence of the coupling chain upon the curvature elasticity which determines the ease with which the director
pattern may be modified using external electric fields [6,7]. although none has considered the systematic variation of
properties with changing coupling chain length for a series of polymers.We shall considered a series of polysiloxane
based side-chain liquid crystal homopolymers in which the coupling chain length is systematically varied. Electro-optic
measurements are used to evaluate the threshold voltages for this series of polymers. Although the variation of
threshold voltage with systematically changing coupling chain length correlates with spares variety of values for similar
polysiloxane based polymers [8,9]. Comparsion is made with existing models of curvature deformation in low molar
mass liquid crystal systems. Where A more modern approach is the elastic continuum theory [10] the LC is considered
as a continuum and molecular details are ignored. Here distortions of a presumed oriented sample are ascribed by the
Frank free energy density. Three types of distortions, twist, splay and bend, can be identified. The response of the
system is then decomposed into terms based on elastic constants. After the synthesis of the first nematic liquid crystal
by L. Gattermann and A. Ritschke, Lehmann found that some liquid crystals behaved differently from others and that a
liquid crystal can be aligned if in contact with a solid surface. This finding is most important for today’s LC-
technology[11]. This theory is primarily used for modeling liquid crystal devices.
II. Materials
Monomers of type [2] (where n=2,3 and 6) These materials have been prepared by Dr.M.J whitcombe at the
department of chemistry, university of reading. [12]. as shown in Scheme 1. For the preparation of the monomer with
n=5, 5-chloropentanol was prepared via reduction of the appropriate acid chloride with LiAIH4 [13]. The use of this
route for the preparation of the monomer with n4 results in cyclisation of the 4-chiorobutanol and hence gives poor
yields for the first step. An alternative procedure to prepare the 4-(4-hydroxybutoxy) benzoic acid was used as detailed
elsewhere [14]. Polymerization of these monomers was performed in deoxygenated chlorobenzene solutions under
reduced pressure at 55°C with 1 mol% AIBN as the initiator. After 24 hours, the resulting polymers were collected by
2. New Electro-Optic Properties of Polysiloxane Liquid Crystals
www.ijeijournal.com Page | 2
precipitation into methanol and purified by repeated precipitation into diethyl ether, followed by drying under reduced
pressure for 48 hours at 100 C. The molecular weight data were obtained by g.p.c. (RAPRA Ltd) at room temperature
with tetrahydrofuran as the eluent. All of these polymers show nematic phases with well defined nematic-isotropic
transition temperatures.
III. Experimental Work
1. Cell preparation
Good alignment is necessary in polymer layers before electro – optic properties can be measured. If this is not
achieved, then the freederricksz transition is observed over arrange of applied field and meaningless data results.
Therefore, efforts have been spent to achieve high quality fabricated electro-optic cells [15]. The typical construction of
an electro – optic cell used experimentally in these investigations is shown in Fig. (2a). Electro-optic cells with
predefined director orientation were constructed from patterned tin oxide coated glass slides (Baltracon Z20). The cell
electrodes, after cleaning in an ultrasonic bath and drying, were coated with a thin layer of a polyimide precursor
consisting of a 5% solution of Rodehftal 322 in dimethylformamide using a spin coater. These coated slides were then
subjected to thermal cycles and a mechanical treatment using a cloth. The selected polymer sample was carefully
applied onto one of the treated glass electrodes and the complete assembly was heated above the clearing point of the
polymer in order to allow the trapped air to escape. The second glass electrode was then mounted above the first
electrode using 0.025 mm thickness Kapton sheet as spacers . The quality of the prealignment treatment was confirmed
through examination of each cell with a polarizing microscope. Complete and uniform director alignment was obtained
by holding the completed electro-optic cell at a temperature 1 0C below the measured clearing point for 10-24 hours.
This technique was successful in inducting a uniform director alignment within the electro-optic cells prepared for all
the materials used in this work. In all cases the predefined director alignment was parallel to the electrode surface and to
the direction of rubbing. The orientational order parameter S for the polymers in the series with n=4,5,6 was measured
as a function of temperature [16].
2. Electro-optic systems:
The most important three devices were used in this work for electro – optic measurement are Mk 100, ALCT,
and HCS 402.The Mk 1000 series temperature controller offers precision, accuracy, and stability for temperature
measurement and control. When coupled with heating / cooling equipment from instc, the Mk 1000 can provide
temperature control, which is accurate to 0.001oC. Two operation modes, keypad operation using the front panel of the
controller, or software control though pc as well as. Adjustable ramp (rate of heating / cooling) to user set temperature
point. Programmable operation command set. Precisely controls temperature to 0.001oC option save temperature data
to the computer. RTD thermistor or thermocouple, LC cell holders for many types of LC cells. ,and ALCT Liquid
Crystal measuring subsystem, which includes ALCT- EO1 (referred as ALCT after), test cell holder, photo detector
head, and connecting cables. Using this system with well prepared LC test cell and proper method, user can measure -
Liquid crystal mixture physical parameters- Optical performance of LCD devices- Application software, WinLC, and
Optical test bench subsystem, which includes light source, polarizer, rotatable hot – cooling stage holder analyzer, and
photo detector holder. and Hot and cold stages Instec was founded over two de eades ago by a group of pioneering
liquid crystal researchers therefore ourm heating and cooling stage system are designed specifically with liquid crystal
applications in mind. We used the device the Hcs402 hot and cold stage is designed to give superior performance in
sample temperature control and other applications. While the Hcs402 provides excellent temperature uniformity, which
is more than sufficient for most applications, there will always be a small vertical temperature gradient between the
bottom heat plate and the sample. The Hcs402is equipped with cable heaters: one located underneath the sample
chamber and other is part of the cover, above the sample chamber. This configuration provides. Thermally uniform
"sample oven" the Hcs402 upper heating element compensates for the temperature gradient by providing and additional
heat source above the sample this is a highly desirable feature when dealing with thicker sample and when spacers are
used to increase the sample chamber height.
Fig. (1). Electro-optic cell.
3. New Electro-Optic Properties of Polysiloxane Liquid Crystals
www.ijeijournal.com Page | 3
HCS 402 devise ALCT devise
MK 1000 devise
Fig. (2). Picture of devices.
Scheme. (3) A schematic representation of the two basic geometries of coupling between the polymer backbone and
the mesogenic side- chain. (a) a parallel or positive coupling, (b) a perpendicular or negative coupling
(a) (b)
Table . (1) Molecular weight and phase transition data determined by using D.S.C in Chemistry
department,university of Reading, U.K
Tni0
cTg0
cDpMnnPolymer
135391805.1×105
61
130401002.0×105
52
12045602×105
43
10052503.2×105
34
8562401.0×105
25
IV. Results
1. Static electro-optic properties
This study is concerned with evaluating the static electro-optic properties for the range of liquid crystal
polymers shown in Table 1 as a function of temperature. By using the experimental arrangement described in the
previous section it was possible to determine the threshold electric field required to distort the surface prealigned
director orientation .In order to achieve complete switching we typically applied 147 to 240 volts (peak to peak) at a
frequency of 500 Hz. Figs.(4a,4b,4c,4d,4e) shows the variation of the transmitted light intensity as a function of the
applied voltage. For The Polymeres (P.1, P.2, P.3, P.4, P.5). For all polymers the dielectric anisotropy is positive. The
electric field deforms an initial planar surface alignment and in this case of the geometry is dominated by the splay
component of the curvature elasticity K11 for small deformations. The threshold voltage Vth is related to the curvature
elasticity, assuming strong anchoring by [17]:
Vth=π(K11/ π0 .ππ)1/2
..….……….… (1)
Where is the anisotropy of the dielectric permittivity, Equation (1). suggests that evaluation of K11 should be a
relatively straightforward procedure. However for a polymer system there are a number of particular problems involved
in the evaluation of Vth , each of which relates to the high viscosity of the polymer. The most important of which is
ensuring that before starting any measurements the sample is in a complete equilibrium state. For each of the samples
considered and for each temperature of measurement we have establish the real relaxation time of the polymer system
through the use of a cyclic electro-optic procedure [18] shown more clearly in Fig.(5) (5a,5b,5c) A plot of ton
for the
indicated temperature showing the variation in ton
for differing values of toff
the time for which the field was left off
prior to the measurement of ton
for a cell prepared using the polymer no. (P.1, P.2, P.3). This type of experiment
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ensures that the relaxation times measured relate to response of the complete system by using a probe, the response time
following the application of an electric field [11]. All threshold voltage measurements were made after the sample had
been held at required temperature for a period of time at least three times the relaxation time.shown more clearly in
Fig.(7) Plots of the measured threshold voltages a function of temperature. As the response time following the
application of small voltages is particularly long we determined the threshold from a plot of the change in the
transmitted optical intensity as a function of the applied small voltage. By extrapolation this method allowed both the
true threshold voltage to be estimated and any dynamic effects to be excluded. To ensure that a steady state was reached
following each voltage step the sample was left for a period between 3 and 5 hours. During this time the transmitted
light intensity was monitored to ensured that the steady state had been achieved.shown more clearly in Fig.(6) A plots
of toff
as a function of the (T – Tg) polymers.(p.1,p.2,p.3) measured using the cyclic electro – optic. Typically at each
stage the sample was held for a period of time ten times longer than the response time. The threshold voltages obtained
in this manner may be related to the curvature elastic constant only if it is valid to assume strong anchoring of the
director at the cell wall. There is a marked reduction in the threshold voltage for both increasing temperature and spacer
length. A similar trend in terms of the of temperature behavior has been observed in the study of a series of copolymers
with n=6 ..The variation of the threshold voltage with systematically changing coupling chain length correlates with
spares variety of values for similar polysiloxane based polymers reported in the literature [19,20].
Fig. (4a)
FigS. (4a, 4b, 4c, 4d, 4e) shows the variation of the transmitted light intensity as a function of the applied voltage. For
The Polymers (P.1, P.2, P.3, P.4, P.5).
Fig. (4b)
Fig. (4c)
5. New Electro-Optic Properties of Polysiloxane Liquid Crystals
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Fig. (4d)
Fig. (4e)
Fig. (5a)
FigS.(5a,5b,5c) A plot of on
for the indicated temperature showing the variation in on
for differing values of off
the
time for which the field was left off prior to the measurement of on
for a cell prepared using the polymer no. (P.1,
P.2, P.3)
Fig. (5b)
6. New Electro-Optic Properties of Polysiloxane Liquid Crystals
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Fig. (5c)
Fig. (6). A plots of off
as a function of the (T – Tg) polymers.(p.1,p.2,p.3) measured using the cyclic electro – optic
Fig. (7).Plots of the measured threshold voltages a function of temperature
Fig. (8). A plots showing square of the threshold voltages against the order parameter S
2. Order parameter
Measurements were made for each sample over a range of temperatures to include both nematic phases, the
resultant order parameter are displayed in Fig. (8).A plots showing square of the threshold voltages against the order
parameter (S).
3. Curvature elasticity
A microscopic understanding of curvature elasticity remains a considerable challenge even in the area of low
molar mass liquid crystalline materials. Existing approaches in the literature are very much first order relating either to
the Maier-Saupe mean field theory [21,22] or developed from the Landau-De Gennes expansion of free energy as a
7. New Electro-Optic Properties of Polysiloxane Liquid Crystals
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function of the order parameter [21,23,24].Saupe and Nebring use the Maier- Saupc approach to establish the
relationship [25,22]:
.…………………(2)
where Vm is the molar volume and cii is temperature independent constant which is a function of the particular
molecule or mesogenic unit. In essence this approach groups all of tie temperature dependence into S2 and Vm
although the latter term varies only slightly over the temperature range considered in this study. We can think of c,1 as
an intrinsic curvature elastic constant. If we take account of the dependence of b.c on S we may combine Equations (1)
and (2) to give [26]:
…………………(3)
where is an intrinsic dielectric anisotropy i.e. that for a perfectly aligned system. If the variation in the threshold
voltage with coupling chain length was due to differences in the level of orientational ordering.
V. Discussion
The variation of the coupling chain length in this series of siloxane based side chain liquid crystal polymers
has impact upon both the phase behavior and upon the electro-optic properties. The increase in the nematic-isotropic
transition temperature with increasing spacer length mirrors similar behavior found in homologous series of low molar
mass liquid crystalline materials [27].In these cases the increase is attributed, at least in a first approach, to the
increasing degree of anisotropy of the mesogenic unit. Of course this is also true of side-chain liquid crystal polymers,
but for such materials there is the added complications arising from the constraints and interactions provided by the
polymer chain. It would be reasonable to assume that as the coupling chain shortened, so the coupling between the
mesogenic unit and the polymer chain would increase. If ordering increases as a result of this coupling, it is natural to
expect the transitions to rise. In practice as shown in (Table 1).the opposite is observed. This suggests that the emphasis
on the role of the polymer chain should be one of constraint than enhanced ordering through coupling. Clearly there is a
subtle balance between these possibilities and small variation can lead to marked effects. there is a strong temperature
dependence of the switching times. In terms of the variation of the nematic-isotropic , variation transition temperature
with spacer length, this appears to have some element of the well-known odd-even effect observed in low molar mass
liquid crystalline materials and in main –chain liquid crystal polymers [28]. The increase in the glass transition
temperature with decreasing spacer length follows expectations based on the restricted motions of the polymer
backbone segments. Clear trends are observed in the threshold voltage variation as a function of both temperature and
spacer length. It is emphasized that considerable care and effort has been taken to exclude from these experiments the
time dependent effects of the high viscosities associated with polymeric liquid crystal systems. In part the increase of
the threshold voltage with decreasing temperature is expected on the basis of an increasing order parameter. The origin
of the variation of the threshold voltage with spacer length is not so clear. It seems reasonable to attribute the increase
of the intrinsic elastic constant to reducmg the spacer length to changing levels of interactions between the mesogenic
units and the polymer backbone. In addition to the systematic variation in the coupling chain there is also some
variation in the degree of polymerisation of this polymer series (Table 1). This could be thought to have some influence
on the electro-optic properties, although there appears to be no pattern in the threshold voltages which matches the
rather random fluctuation of the molecular weight data shown in Table I. We have previously reported some threshold
voltage measurements for a series of methylmcthacrylatce based side-chain liquid crystal polymers with differing
molecular weights [29]. There was a distinct variation in the threshold voltage hut this was only really significant for
materials with a degree of polymerisation of less than 50. For the CBZ6 polymer a variation of the degree of
polymerisation from 50 to 300 resulted in an increase of the threshold voltage of only < 10% [22]. We can safely
conclude therefore that the trends seen in the data reported here are truly a reflection of the role of the length of the
spacer chain.
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