This research article describes a study using multi-angle laser light scattering to determine the molecular weights of two polystyrene polymer solutions. The molecular weights measured were 388,300±16,500 g/mol and 915,300±44,800 g/mol, which were within 2.7% of the known values for the solutions. The article provides background on static light scattering analysis and the Zimm plot method used to calculate molecular weight and radius of gyration from light scattering intensity measurements taken at varying angles.
Evaluation of mechanical and thermal properties of microwave irradiated poly ...Mukarram Zubair
Poly (styrene-co-methyl methacrylate) (P(S-co-MMA)) was blended with pristine graphene (G) by melt mixing technique and treated under microwave irradiation. The nanocomposites were irradiated for 5 and 10 min at frequency 1245 MHz.
Structure changes in the irradiated nanocomposites were observed by Fourier transform infrared spectroscopy and Raman spectroscopy. The irradiated composites showed a significant increase in the storage modulus i.e. 21% for 0.1% and 31% for
1% graphene polymer composites after 5 min irradiation. However at higher irradiation (10 min), degradation of nanocomposites was observed. The concept of improvement of interfacial interaction between graphene and P(S-co-MMA) chains at 5-min microwave exposure and degradation of nanocomposites at higher irradiation duration was assessed and supported by X-ray diffraction and scanning electron
microscopy.
A Study of Some Optical Properties of Chromic Chloride(퐂퐫퐂퐥ퟑ )Thin FilmQUESTJOURNAL
ABSTRACT: In this work,the optical properties of chromic chloride(푪풓푪풍ퟑ )thin film prepared at different thickness has been measured. The relationship between transparency, absorbance and photon energy for the prepared samples has been studied. It has been found, the behavior of curves is the same for each samples.Moreover, it has been observed thatThe best fit of theexperimental curve to a band gap function was obtained for 푛 = 2 to direct bandgap energy values the obtained values are 1.531 eV, 1.533 eV,1.536 eV, and 1.539 eV for dip the rated of 퐶푙 (0.0 - 0.25 – 0.50 and 0.75 ) respectively.
Study of Structural and Dielectric properties of BaTiO3 Doped with Mg-Cu-Zn F...IJSRD
The magnetoelectric (ME) composites having the general formula, (x) Mg0.25Cu0.25Zn0.5Fe2O4 + (1-x) BaTiO3 (x=15%, 30%, 45%) were synthesized by sintering mixtures of highly ferroelectric BaTiO3 and highly magnetostrictive magnetic component Mg0.25Cu0.25Zn0.5Fe2O4. The presence of constituent phases of ferrite, ferroelectric and their composites were confirmed by X-ray diffraction (XRD) studies. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM), which revealed uniform mixing of two phases. The variations in dielectric constant and dissipation factor as a function of frequency from 100 Hz to 1 MHz were measured in a Hioki LCR Hi-Tester. The dielectric constant and dielectric loss were found to decrease rapidly in the low frequency region and became almost constant in the high frequency region. The electrical conductivity deduced from the measured dielectric parameters has been analyzed and found that the conduction mechanism in these composites is in conformity with small polaron hopping model.
Evaluation of mechanical and thermal properties of microwave irradiated poly ...Mukarram Zubair
Poly (styrene-co-methyl methacrylate) (P(S-co-MMA)) was blended with pristine graphene (G) by melt mixing technique and treated under microwave irradiation. The nanocomposites were irradiated for 5 and 10 min at frequency 1245 MHz.
Structure changes in the irradiated nanocomposites were observed by Fourier transform infrared spectroscopy and Raman spectroscopy. The irradiated composites showed a significant increase in the storage modulus i.e. 21% for 0.1% and 31% for
1% graphene polymer composites after 5 min irradiation. However at higher irradiation (10 min), degradation of nanocomposites was observed. The concept of improvement of interfacial interaction between graphene and P(S-co-MMA) chains at 5-min microwave exposure and degradation of nanocomposites at higher irradiation duration was assessed and supported by X-ray diffraction and scanning electron
microscopy.
A Study of Some Optical Properties of Chromic Chloride(퐂퐫퐂퐥ퟑ )Thin FilmQUESTJOURNAL
ABSTRACT: In this work,the optical properties of chromic chloride(푪풓푪풍ퟑ )thin film prepared at different thickness has been measured. The relationship between transparency, absorbance and photon energy for the prepared samples has been studied. It has been found, the behavior of curves is the same for each samples.Moreover, it has been observed thatThe best fit of theexperimental curve to a band gap function was obtained for 푛 = 2 to direct bandgap energy values the obtained values are 1.531 eV, 1.533 eV,1.536 eV, and 1.539 eV for dip the rated of 퐶푙 (0.0 - 0.25 – 0.50 and 0.75 ) respectively.
Study of Structural and Dielectric properties of BaTiO3 Doped with Mg-Cu-Zn F...IJSRD
The magnetoelectric (ME) composites having the general formula, (x) Mg0.25Cu0.25Zn0.5Fe2O4 + (1-x) BaTiO3 (x=15%, 30%, 45%) were synthesized by sintering mixtures of highly ferroelectric BaTiO3 and highly magnetostrictive magnetic component Mg0.25Cu0.25Zn0.5Fe2O4. The presence of constituent phases of ferrite, ferroelectric and their composites were confirmed by X-ray diffraction (XRD) studies. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM), which revealed uniform mixing of two phases. The variations in dielectric constant and dissipation factor as a function of frequency from 100 Hz to 1 MHz were measured in a Hioki LCR Hi-Tester. The dielectric constant and dielectric loss were found to decrease rapidly in the low frequency region and became almost constant in the high frequency region. The electrical conductivity deduced from the measured dielectric parameters has been analyzed and found that the conduction mechanism in these composites is in conformity with small polaron hopping model.
Adhesion of Photon-driven Molecular Motors to Surfaces via 1,3-dipolar Cycloa...Gregory Carroll
We report the attachment of altitudinal light-driven molecular motors to surfaces using 1,3-
dipolar cycloaddition reactions. Molecular motors were designed containing azide or alkyne groups for attachment
to alkyne- or azide-modified surfaces. Surface attachment was characterized by UVvis, IR, XPS, and ellipsometry
measurements. Surface-bound motors were found to undergo photochemical and thermal isomerizations
consistent with unidirectional rotation in solution. Confinement at a surface was found to reduce the rate of the
thermal isomerization process. The rate of thermal isomerization was also dependent on the surface coverage of
the motors. In solution, changes in the UVvis signal that accompany thermal isomerization can be fit with a
single monoexponential decay. In contrast, thermal isomerization of the surface-bound motors does not follow a
single monoexponential decay and was found to fit a biexponential decay. Both one- and two-legged motors were
attached to surfaces. The kinetics of thermal isomerization was not affected by the valency of attachment,
indicating that the changes in kinetics from solution to surface systems are related to interactions between the
surface-bound motors.
ELECTRICAL PROPERTIES OF NI0.4MG0.6FE2O4 SYNTHESIZED BY CONVENTIONAL SOLID-ST...IAEME Publication
Ni0.4Mg0.6Fe2O4 samples are prepared by conventional double sintering approach and sintered at 1300oC/ 2 h. These ferrites are characterized using X-ray diffractometer. The diffraction study reveals that the present compound shows perfect single phase cubic spinel structure. In addition, the behavior of distinct electrical properties such as dielectric constant (ε'), dielectric loss (ε") and ac-conductivity (σac) as a function frequency as well as temperature is analyzed using the LCR controller
Investigation of the Effects of Fullerene addition and Plasma Exposure on Opt...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.
Preparation of lithium ferrite nanoparticles by high energy ball milling and ...IJERA Editor
Ferrites are ferrimagnetic ceramic materials with inherent useful electromagnetic properties. Of them, spinelstructured ferrites are promising materials for microwave device applications; stress/torsion sensors and energy storage applications like anode materials in lithium batteries, fuel cells, solar cells etc. Nanostructured spinels further have high and wide scope of potential applications. In the present study, two different types of varied sized ferrimagnetic lithium ferrite spinel nanoparticles prepared using chemical sol-gel auto-combustion method were chosen. The prepared spinel particles were heated at 300°C for 1h. After heating the powders were milled using a High Energy Ball Mill for 30 minutes to further grind the particles and then subjected to various characterizations. Structural characterization was done using X-Ray Diffraction Method (XRD). The study revealed the spinel structure of these samples. Structural parameter such as lattice constant was determined using XRD data and found that the lattice parameter agrees with the standard data. DLS study found the agglomerations of the nanoparticles. The synthesized nanospinel particles were also characterized by the UVVis Spectroscopy, the Fourier Transform Infrared Spectroscopy (FTIR). Finally the magnetic hysteresis properties were studied using a Vibrating Sample Magnetometer (VSM)
Plasma treatment is used to modify and improve the surface conditions of various materials. The use of plasma technology on plastic and composite carbon substrates enables these heat-sensitive materials to be successfully coated with ultraviolet (UV) curable powder coatings.
Adhesion of Photon-driven Molecular Motors to Surfaces via 1,3-dipolar Cycloa...Gregory Carroll
We report the attachment of altitudinal light-driven molecular motors to surfaces using 1,3-
dipolar cycloaddition reactions. Molecular motors were designed containing azide or alkyne groups for attachment
to alkyne- or azide-modified surfaces. Surface attachment was characterized by UVvis, IR, XPS, and ellipsometry
measurements. Surface-bound motors were found to undergo photochemical and thermal isomerizations
consistent with unidirectional rotation in solution. Confinement at a surface was found to reduce the rate of the
thermal isomerization process. The rate of thermal isomerization was also dependent on the surface coverage of
the motors. In solution, changes in the UVvis signal that accompany thermal isomerization can be fit with a
single monoexponential decay. In contrast, thermal isomerization of the surface-bound motors does not follow a
single monoexponential decay and was found to fit a biexponential decay. Both one- and two-legged motors were
attached to surfaces. The kinetics of thermal isomerization was not affected by the valency of attachment,
indicating that the changes in kinetics from solution to surface systems are related to interactions between the
surface-bound motors.
ELECTRICAL PROPERTIES OF NI0.4MG0.6FE2O4 SYNTHESIZED BY CONVENTIONAL SOLID-ST...IAEME Publication
Ni0.4Mg0.6Fe2O4 samples are prepared by conventional double sintering approach and sintered at 1300oC/ 2 h. These ferrites are characterized using X-ray diffractometer. The diffraction study reveals that the present compound shows perfect single phase cubic spinel structure. In addition, the behavior of distinct electrical properties such as dielectric constant (ε'), dielectric loss (ε") and ac-conductivity (σac) as a function frequency as well as temperature is analyzed using the LCR controller
Investigation of the Effects of Fullerene addition and Plasma Exposure on Opt...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.
Preparation of lithium ferrite nanoparticles by high energy ball milling and ...IJERA Editor
Ferrites are ferrimagnetic ceramic materials with inherent useful electromagnetic properties. Of them, spinelstructured ferrites are promising materials for microwave device applications; stress/torsion sensors and energy storage applications like anode materials in lithium batteries, fuel cells, solar cells etc. Nanostructured spinels further have high and wide scope of potential applications. In the present study, two different types of varied sized ferrimagnetic lithium ferrite spinel nanoparticles prepared using chemical sol-gel auto-combustion method were chosen. The prepared spinel particles were heated at 300°C for 1h. After heating the powders were milled using a High Energy Ball Mill for 30 minutes to further grind the particles and then subjected to various characterizations. Structural characterization was done using X-Ray Diffraction Method (XRD). The study revealed the spinel structure of these samples. Structural parameter such as lattice constant was determined using XRD data and found that the lattice parameter agrees with the standard data. DLS study found the agglomerations of the nanoparticles. The synthesized nanospinel particles were also characterized by the UVVis Spectroscopy, the Fourier Transform Infrared Spectroscopy (FTIR). Finally the magnetic hysteresis properties were studied using a Vibrating Sample Magnetometer (VSM)
Plasma treatment is used to modify and improve the surface conditions of various materials. The use of plasma technology on plastic and composite carbon substrates enables these heat-sensitive materials to be successfully coated with ultraviolet (UV) curable powder coatings.
is an SaaS based multi-level, innovative skills
assessment platform which helps an organization in pre-hire screening, Training, Certification Test and
Online Examination.
this is summer internship program project, this projects helps for the promotional activities and strategies used by the company. i referred some of the project to develop this project. this includes literature review and marketing mix and promotional mix strategies. this project also included with home loans industry in india
In order to introduce myself, as a hard worker and team player, who already has some strong experience as a Process Control Engineer, hereby I’d like to present in a summary manner my background and expertise, while stating my willingness to contribute with my employers in achieving goals and reaching high levels of quality and profitability in business.
Thanks in advance for your interest in my profile.
Regards.
Fernando Vasquez.
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
State of the Art in the Characterization of Nano- and Atomic-Scale CatalystsDevika Laishram
Nanometer and subnanometer particles and films are becoming an essential and
integral part of new technologies and inventions in different areas. Some of the
most common areas include the microelectronic industry, magnetic recordings,
photovoltaic applications, and optical coatings. Because of the ultrasmall size at
atomic levels, the effect of quantum size becomes prominent, and the sensitivity
of size is defined even by a difference of a single atom. Additionally, the effect
is of utmost importance as the single-atom catalysts are far more advantageous
than conventional catalysts as they tend to anchor easily because of their low
coordination. Also, the presence of a single-atom catalyst in reactions creates
efficient charge transfer as it forms a strong interaction with the support.
Furthermore, catalysts in the subnanometer regime exhibit different electronic
states and adsorption capabilities compared to traditional catalysts. Therefore, to
fully appreciate the subnanometer catalysis reactions, it is essential to study the
means of characterizing the prepared subnano catalysts,
This presentation dives into the deep realms of nano-chemistry starting from the very basics to a sufficient advanced level. Nano-chemistry has always been a very intriguing topic for most of us as we see it in movies more than frequently. If not, we at least hear some explanation about a curious event that relates directly to nano-chemistry.
Diving into the depths of those explanations related to nano-chemistry and revealing the actual facts about nano-chemistry and its related topics. We have formulated this presentation to become a crucial source of information regarding nano-chemistry and its other related terms.
It is also a study material for Basics of Chemistry subject taught during the 1st or 2nd semesters during B.E. / B.Tech degree courses.
Interaction of Components in Molecular Optoelectronics for the Next Generati...Scientific Review SR
The interaction of molecular optoelectronic components on the molecular scale were studied where
the solvent shell indicating the influence of the medium was found to be surprisingly small. The transport of
energy as resonant energy transfer covers distances of about 5 nm and was shown not to proceed by a simple to
dipole dipole interaction with typical restrictions, but by a more complex mechanism. Furthermore, a novel -type of
far-reaching interactions of electronically excited structures until macroscopic dimensions were fond and may be
applied for addressing molecular structures by conventional electronics
A quantitative numerical model of multilayer vapor deposited organic light em...AjayaKumar Kavala
A one-dimensional numerical model for the quantitative simulation of multilayer organic light
emitting diodes ~OLEDs! is presented. It encompasses bipolar charge carrier drift with
field-dependent mobilities and space charge effects, charge carrier diffusion, trapping, bulk and
interface recombination, singlet exciton diffusion and quenching effects. Using field-dependent
mobility data measured on unipolar single layer devices, reported energetic levels of highest
occupied and lowest unoccupied molecular orbitals, and realistic assumptions for experimentally not
direct accessible parameters, current density and luminance of state-of-the-art undoped
vapor-deposited two- and three-layer OLEDs with maximum luminance exceeding 10000 cd/m2
were successfully simulated over 4 orders of magnitude. For an adequate description of these
multilayer OLEDs with energetic barriers at interfaces between two adjacent organic layers, the
model also includes a simple theory of charge carrier barrier crossing and recombination at organic–
organic interfaces. The discrete nature of amorphous molecular organic solids is reflected in the
model by a spatial discretization according to actual molecule monolayers, with hopping processes
for charge carrier and energy transport between neighboring monolayers.
Photophysical properties of light harvesting molecules: three different approaches (of increasing complexity and accuracy) to foresee the harvesting behaviour are reviewed with a highly didactic flow. Design principles are highlighted.
A supplementary set of slides is available among my uploads.
This document is a self-made research I did for a photochemistry course. I don't own part of the shown material and references for many public images are reported at the end.
Graphene Quantum Dots-Based Composites for Biomedical Applicationsnooralam814309
Carbon derivatives, such as graphene-based nanocomposites, have garnered significant global attention
due to their remarkable optical and electrical properties. In this study, the authors examined nanohybrid
materials based on graphene quantum dots (GQDs) for biomedical applications. The biocompatibility
of GQDs makes them ideal materials for a range of medical applications, including biosensing, drug
delivery, and various therapeutic uses. The authors also addressed issues related to controlled production and composites involving GQDs. Similarly, they discussed factors that affect the applicability and
viability of these materials
Computational Chemistry aspects of Molecular Mechanics and Dynamics have been discussed in this presentation. Useful for the Undergraduate and Postgraduate students of Pharmacy, Drug Design and Computational Chemistry
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.
Similar to Chen_Peterson_multi_angle_light_scattering_2015 (20)
Impact of Gamma Irradiation on Structural and Dielectric Properties of CuI-PV...
Chen_Peterson_multi_angle_light_scattering_2015
1. Research Article Applied Optics 1
Multi-angle laser light scattering: determining the
molecular weight of polymers
TYLER PETERSON1,* AND QIANTING CHEN1,*
1Applied Optics Track, Graduate Internship Program, University of Oregon, 1252 University of Oregon, Eugene OR 97403
*Corresponding authors: tbp@uoregon.edu; qchen3@uoregon.edu
Compiled September 7, 2015
Molecular weight and size, or radius of gyration, are two properties that are commonly used to charac-
terize polymers. Static light scattering analysis is an absolute method to obtain these measurements. In
this experiment, two polystyrene standard solutions were examined, having molecular weights of 382,000
g/mol and 891,000 g/mol, using a Wyatt Dawn Enhanced Optical System. The measured molecular weights
were 388,300±16,500 g/mol and 915,300±44,800 g/mol, both within 2.7% of the known values.
OCIS codes: (290.5820) Scattering measurements
Polymers are macromolecules whose chemical structures
are composed of repeating units. The ability to specifically
arrange these repeat units allows for the optimization of a given
polymer material for an array of purposes. As early as 1600
B.C.E., ancient Mesoamerican civilizations had unintentionally
discovered the wide range of applications polymer materials
have. Rubber balls were used often for sporting events, liquid
rubber was used for writing and painting, and rubber bands
were used to fasten stone ax heads to wooden handles. Chemical
analysis of these materials has shown the main ingredients to
be latex acquired from the Castilla elastica tree and juice from
Ipomoea alba, a species of morning glory vine. On its own,
latex becomes too brittle to retain its shape upon drying, but
the Mesoamerican peoples discovered that the added juice
counteracted this material shortcoming. Modern mechanical
analysis has shown increased strength and elasticity in these
items as a result of the purification of latex, a natural polymer,
within the material [1].
The first instance of a more controlled approach to manu-
facturing polymers came in 1841, when Charles Goodyear’s
process of vulcanization was successfully implemented [2].
The idea came to Goodyear after accidentally bringing a
rubber sample into contact with a hot stove and observing
a charring effect similar to leather, which inspired him to
investigate the effect of heat on similar compounds [4]. The
crosslinking induced by the addition of sulfur atoms to polymer
backbone chains through the vulcanization process yields
enhanced modulus of elasticity, tensile strength, and resistance
to degradation by oxidation [5]. Wide scale production of
polymer materials did not really take off, however, until 1910,
when Leo H. Baekeland invented Bakelite, a combination of
phenol and formaldehyde that could be thermoset to hold any
form. The increased applicability inspired Baekeland to market
his product as the “Material of a thousand Uses” [6]. While
Bakelite eventually fell from the spotlight as the material of
choice, Baekeland is still considered the true father of synthetic
plastics. In today’s world, countless products are made from
polymer materials. Possibly the largest number of them fall
into the category of plastics, having a large variety of different
property combinations. Plastics are found everywhere, from
polycarbonate safety helmets and photographic film, to acrylic
aircraft enclosures. Elastomers, or rubbers, are polymers that
have a characteristic elasticity, or the ability to be deformed
drastically and spring back to their original form. Fibers are the
third major category of polymers, describing materials that can
be drawn into very long filaments which are typically used in
the textile industry for the manufacturing of clothing [5].
The microstructure of polymers is what determines the
macroscopic behavior of synthesized materials. The ability to
finely adjust this microstructure is what allows engineers to
design materials for very specific purposes, but it is important to
ensure that the synthesized polymer has the intended properties.
During the polymerization process, molecules can form very
short or long polymer chains, so the molecular weight is a
good starting point for characterization. For example, tensile
strength, elasticity, resistance to deformation, and many other
mechanical properties are dependent on molecular weight, so
its accurate determination can be crucial in the engineering
process [7]. Static light scattering is one technique through
which this property may be determined, and is the focus of this
study. Polymer molecules, when mixed in a solution that is
illuminated by a laser, will gain an induced dipole moment and
begin to emit light through a process known as scattering. In
static light scattering, this emitted light is collected at a range of
2. Research Article Applied Optics 2
angles and analyzed to determine the average radius of gyration
and weight average molar mass of the molecules.
When light interacts with matter, five different phenomena
take place, depending the size of that matter: absorption,
reflection, diffraction, refraction, and scattering [8]. When
considering matter on the scale of polymer macromolecules,
scattering effects dominate these interactions. Observing the
resultant scattering patterns can be very indicative of the size
and structure of macromolecules, as described by the measured
values for both the weight average molecular weight and the
RMS radius of gyration [9].
Light scattering is a process by which electromagnetic
waves incident on a material induce electron oscillations within
that material, which then act as independent emitters of light.
Because the induced electron oscillations are dependent on
the frequency of the incident waves, the emitted light will
have that same frequency. In addition, this scattering is elastic,
so no absorption takes place. Such behavior is known as
Rayleigh scattering, and is taken advantage of heavily in the
characterization of polymers [10].
The intensity of scattered light is a good measure to use for
experimentally determining the molecular weight of polymer
macromolecules [3]. When a laser is incident upon multiple,
unconnected molecules, the induced oscillations will not
necessarily be in phase, resulting in incoherent scattered light,
which reduces the intensity. With increased molecular weight,
however, these molecules will be chained together to form larger
polymers. This forces all of the charge within the polymer to
subsequently oscillate in phase, thus providing a more intense
scattered beam [15].
The architecture of the polymer can be implied from the
angular dependence of the intensity of scattered light. Because
the individual monomers will act as emitters of light, an interfer-
ence pattern will manifest from the polymer as a whole [15]. By
collecting light at multiple angles, this angular dependence may
be observed. Both the weight average molecular weight and
RMS radius of gyration can be obtained by constructing a Zimm
plot. Zimm plots are created using the following equation [13]:
Rθ
K∗c
= MP(θ) − 2A2cM2
P2
(θ) (1)
Where c is the concentration of the solute molecules in the
solvent (g/mL), M is the weight average molar mass (g/mol),
A2 is the second virial coefficient (mol mL / g2) (a measure of
how good the polymer-solvent relationship is), P(θ) is a form
factor dependent on the size and shape of the polymer, and the
Rayleigh ratio, Rθ, which is defined by [13]:
Rθ = Nθ ACSCC(
Vθ − Vθ,baseline
Vlaser − Vlaser,dark
) (2)
Where ACSCC is defined as the configuration specific
calibration constant. This constant depends on the type of
solvent and flow cell being used, whose determination will be
described shortly. Vθ, Vθ,baseline, Vlaser, and Vlaser,dark relate to
voltages output by photodetectors at different angles with the
laser turned on and turned off, which will be elaborated on in
the section regarding calibration. The Zimm equation is also
dependent on the optical constant, K*, which is defined by [13]:
K∗
=
4π2n2
0(dn
dc )2
λ2
0NA
(3)
Where dn/dc is the relative change in index of refraction
with respect to the change in solution concentration, λ0 is the
wavelength of incident light, NA is Avogadro’s number, and n0
is the index of refraction of the solvent in vacuum.
While there are many different fits to characterize light
scattering patterns, such as the Debye, Berry, and Random Coil
fits, the Zimm fit is the most accurate for particles whose radius
is between 20 – 50 nm. The polystyrene standards used in this
experiment fell in this size range, so the other fits are out of the
scope of this report.
A Wyatt DAWN Enhanced Optical System (EOS) is the
multi-angle static light scattering instrument that was used to
run the experiment. The sample under consideration is pumped
into a flow cell contained within the instrument from a glass
syringe using an infusion pump. A laser of wavelength 780.88
nm, as measured by a spectrometer, illuminates the sample.
The emitted light from this process is collected by 18 hybrid
transimpedance photodetectors surrounding the sample, which
convert the scattered light intensity into voltages that may be
analyzed.
ASTRA 4.90, provided by Wyatt Technology, was the
software used to collect and analyze data from the DAWN EOS.
Four main steps are taken to obtain molecular weight, radius
of gyration, and second virial coefficient information. First,
the instrument must be calibrated in order to determine the
Rayleigh ratio. A beam splitter placed before the sample yields
the incident light intensity, which is then compared against the
scattered intensities. To correct for ambient light, the laser is
then turned off and the voltages measured by the photodetectors
are used to determine the dark offset, which will be subtracted
from final measurements. Once this is complete, a normalization
is carried out to ensure the detectors are operating properly
in conjunction with each other. A low molecular weight, high
concentration polymer solution is injected into the flow cell.
The solvent in this step must be the same solvent that will be
used to mix solutions for analysis. A low molecular weight
polymer must be used to ensure that it will scatter isotropically,
which will be the case for any molecule with a radius below
10 nm [13]. The geometry of the flow cell is such that each
detector is aligned to view a different scattering volume, which
is defined as the intersection between an incident beam of light
and the scattered beam of light. Because scattered intensity is
proportional to the scattering volume, each detector will report
a slightly different voltage. This, along with refraction effects,
is accounted for by a set of normalization coefficients for the
detectors produced by the normalization collection. After the
detectors have been calibrated and normalized, the instrument
is ready to collect data on the sample under consideration.
3. Research Article Applied Optics 3
A higher molecular weight polymer solution is mixed at a
number of different concentrations, which are introduced to
the system from highest to lowest concentration. A collection
is run on each concentration, resulting in a step-like total data
collection. This information is then converted into a Zimm
plot by entering the concentrations into the software. Once
these four steps have been completed, the calculated molecular
weight, RMS radius of gyration, and second virial coefficient
for the polymer is output. To yield the best results, a number of
measurements must be taken to minimize error.
Cleanliness is incredibly important in light scattering mea-
surements. The scattered intensity of a particle is proportional
to the sixth power of its radius, so any excess particulates in
the solution will nullify a data collection. To avoid this, an
acid-base wash was carried out for all scintillation vials used
to mix solutions. In addition, solvents were filtered before
solution mixing, and mixed solutions were filtered out of the
syringe immediately prior to entering the DAWN EOS. Also
important is the degree to which the concentrations of mixed
solutions are known. To ensure optimal accuracy in this regard,
all solutions should be weighed out by mass on an analytical
balance. Vibrations in the system will produce inconsistent
scattered intensities, so measurements should be carried out in
isolation from other scientists working in the same laboratory.
Samples, once injected, should be allowed to settle for sufficient
time for similar reasons. A sample was considered to be fully
settled when fluctuations in the 90 ◦ detector output voltage fell
below 0.02 V. Finally, the laser must be allowed adequate time to
reach thermal equilibrium. This was observed to take between
two to three hours, as determined by the signal stability in
measurements.
The experiment measured a polystyrene standard with
a molecular weight of 382,000 g/mol. We measured two
concentrations, 0.106 mg/mL and 0.479 mg/mL. The Zimm
plot in Fig. 1 reported the light scattering molecular weight of
this sample to be 388,300±16,500 g/mol, an error of 1.6% from
the known value. The radius of gyration was reported to be 0
nm for this solution, which we predict is due to errors in the
calibration and normalization constants.
Fig. 1. The Zimm plot of a polystyrene standard with molecu-
lar weight of 382,000 g/mol.
To check the reproducibility of our experiment, another
measurement was performed with a polystyrene standard
having molecular weight of 891,000 g/mol. We measured
two concentrations again, 0.101 mg/mL and 0.248 mg/mL.
The Zimm plot in Fig. 2 reported the molecular weight of this
sample to be 915,300±44,800 g/mol, an error of 2.7% from the
known value. The radius of gyration for this polymer solution
was reported to be 33.5±3.8 nm.
Fig. 2. The Zimm plot of a polystyrene standard with molecu-
lar weight of 891,000 g/mol.
The molecular weight of a polymer is an integral property
in determining how a material made from that polymer will
behave on a macroscopic scale. Therefore, being able to
measure it with high levels of accuracy is essential to ensure the
engineered material will perform as expected. Examining how
the polymer scatters light when illuminated by a laser is one
way to determine its molecular weight, as well as its molecular
architecture via the radius of gyration. A Wyatt DAWN EOS
static light scattering instrument was utilized to carry out
measurements on various polystyrene solutions, using toluene
as the solvent. Molecular weights were determined to within 3%
of the known values for two different polystyrene standards.
The immediate future direction of this experiment will
include further data collection on known polymer standards to
solidify reproducible procedural methods. A gel permeation
chromatography instrument will then be integrated in-line with
the DAWN EOS to reduce polydispersity in the samples yield
more accurate weight average molecular weights and radii of
gyration. Once a consistent procedure has been demonstrated,
the experimental setup will be used in collaboration with
polymer chemists and chemical engineers to test unknown
polymer and nanoparticle solutions for industry applications.
ACKNOWLEDGMENTS
We would like to acknowledge Dr. Chartoff and Dr. Check from
the University of Oregon Polymer Characterization Laboratory
for allowing access to their facilities for the duration of this
experiment, as well as for providing guidance along the way.
Chris Lundeen and Matthew Williams are polymer chemistry
students who collaborated on this project, lending chemistry-
specific advice and perspective the whole way through. Finally,
Dr. Nima Dinyari for establishing the collaboration between
the Optics and Polymer programs that allowed this project to
take place, in addition to acting as a mentor throughout the
experiment.
4. Research Article Applied Optics 4
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