Thesis (Ph.D.)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Yulin Deng; Committee Member: Arthur Ragauskas; Committee Member: Jeff Empie; Committee Member: Jeffery Hsieh; Committee Member: Preet Singh

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Ronald Rousseau; Committee Co-Chair: Athanassios Sambanis; Committee Member: Amyn Teja; Committee Member: Athanasios Nenes; Committee Member: Ingeborg Schmidt-Krey. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Interactions between polysaccharide derivatives and rod-like cellulose nanocrystals were studied by light scattering. Two replicates of cellulose nanocrystals (DOE-2-12A and DOE-2-12B) were probed with polarized and depolarized dynamic light scattering. X-ray photoelectron spectroscopy experiments showed sulfate groups on cellulose nanocrystals. Decay rates from polarized dynamic light scattering experiments exhibited a significantly smaller angular dependence for both samples. However, DOE-2-12B showed a smaller angular dependence than DOE-2-12A. Lengths and diameters of DOE-2-12A and DOE-2-12B obtained by Broersma's formula were 229 " 19 and 19 " 7 nm and 240 " 18 and 22 " 6 nm, respectively. The resultant length and diameter of DOE-2-12B were comparable to those for cellulose whiskers obtained from cotton. Adsorption of pullulan 4-chlorocinnamate (P4CC03) onto cellulose nanocrystals (DOE-2-12B) was also studied by UV-Vis spectroscopy, zeta-potential measurements, and polarized and depolarized dynamic light scattering. UV-Vis spectroscopy of the P4CC03/water binary system and in situ light scattering showed UV crosslinking of pullulan 4-chlorocinnamate occurred in binary and ternary systems but led to different aggregation behavior in the two ternary systems: PreX where P4CC03 crosslinking occurred prior to the addition of cellulose nanocrystals and Rxn where cellulose nanocrystals were present during UV exposure. These studies showed P4CC03 adsorbed onto cellulose nanocrystals and UV induced crosslinking occurred at the surface of the cellulose nanocrystals. Zeta-potential measurements also showed that P4CC03 adsorbed onto cellulose nanocrystals. Finally, adsorption of 2-hydroxypropyltrimethylammonium xylans (HPMAXs) of degree of molar substitution MS = 0.34 onto rod-like cellulose nanocrystals (DOE-2-12Bs) were probed with zeta-potential measurements and polarized and depolarized dynamic light scattering. Zeta-potential changes of HPMAX/water, HPMAX/DOE-2-12B/water, and DOE-2-12B/water systems showed HPMAX adsorption onto DOE-2-12Bs. Intensity autocorrelation functions from Hv and Vv mode exhibited partial heterodyning. Decay time distributions of the binary and ternary systems showed that aggregates existed in the binary system but disappeared in the ternary system. These observations revealed that HPMAX adsorbed onto a fraction of the cellulose nanocrystals in the ternary system at low concentrations of HPMAX. Decreasing translational and rotational diffusion coefficients with increasing HPMAX concentration indicated HPMAX adsorption onto cellulose nanocrystals. A significant HPMAX concentration dependence of the ratio of rotational diffusion coefficient to translational diffusion coefficient showed strong adsorptive interactions between HPMAX and DOE-2-12B. These studies showed there were interactions between polysaccharides and cellulose nanocrystals even in very dilute solutions. Also, it was shown that probe diffusion studies with rod-like cellulose nanocrystals is a promising strategy for probing complicated polymer solutions. / Ph. D.

No description available.

The interaction between coherent waves and material systems with complex optical properties is a complicated, deterministic process. Light that scatters from such media gives rise to random fields with intricate properties. It is common perception that the randomness of these complex fields is undesired and therefore is to be removed, usually through a process of ensemble averaging. However, random fields emerging from light matter interaction contain information about the properties of the medium and a thorough analysis of the scattered light allows solving specific inverse problems. Traditional attempts to solve these kinds of inverse problems tend to rely on statistical average quantities and ignore the deterministic interaction between the optical field and the scattering structure. Thus, because ensemble averaging inherently destroys specific characteristics of random processes, one can only recover limited information about the medium. This dissertation discusses practical means that go beyond ensemble averaging to probe complex media and extract additional information about a random scattering system. The dissertation discusses cases in which media with similar average properties can be differentiated by detailed examination of fluctuations between different realizations of the random process of multiple scattering. As a different approach to this type of inverse problems, the dissertation also includes a description of how higher-order field and polarization correlations can be used to extract features of random media and complex systems from one single realization of the light- iv matter interaction. Examples include (i) determining the level of multiple scattering, (ii) identifying non-stationarities in random fields, and (iii) extracting underlying correlation lengths of random electromagnetic fields that result from basic interferences. The new approaches introduced and the demonstrations described in this dissertation represent practical means to extract important material properties or to discriminate between media with similar characteristics even in situations when experimental constraints limit the number of realizations of the complex light-matter interaction

Protein aggregation is a phenomenon that plays a major role in protein crystallization and in protein formulation. In protein crystallization, aggregation is the prerequisite step; however, in protein formulation it has to be suppressed to assure therapeutic efficiency of the product. Light scattering techniques are the most promising methods to study the hydrodynamic properties of macromolecular solutions, which directly measures protein aggregation. Unfortunately, the normal dynamic light scattering technique is regarded as expensive because of the amount of protein used for these experiments. In order to address this problem, a scale down dynamic light scattering device has been designed. The osmotic second virial coefficient, a dilute solution parameter helps in identifying solution conditions for protein crystal growth. The second part of this thesis involves comparison of osmotic second virial coefficient (B) measurements of lysozyme using laser light scattering techniques with B measurements of lysozyme performed using self-interaction chromatography (SIC).

No description available.

Keratin is a biomaterial derived from biological sources and can be used in a variety of medical applications. This study focuses on keratin derived from human hair. Unfortunately, there is not a lot of information in the literature describing how keratin reacts to subtle changes in an aqueous solution such as differences in pH, keratin concentration, buffer concentration, salt concentration, and temperature. To have a better understanding of this effect, dynamic light scattering was used to test the size ranges and volume percentages in each range. Dynamic light scattering shows the size of the keratin in each environment and its consistency with time. The results showed that there is a difference in keratin behavior between water and buffer solutions, but very subtle differences between each buffer, buffer concentration, keratin concentration, pH and temperature. Keratins aggregate extensively in un-buffered conditions (i.e. pure water), which has implications to both purification and fabrication of biomaterials as water is used extensively in these processes. Interestingly, there was little effect of keratin concentration, pH, and temperature on the buffers used in this study, suggesting there may be a wide range of conditions in which aggregation can be minimized. / Master of Science

Monodispersed microgels composed of poly-acrylic acid (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) interpenetrating networks were synthesized by 2-step method with first preparing PNIPAM microgel and then polymerizing acrylic acid that interpenetrates into the PNIPAM network. The semi-dilute aqueous solutions of the PNIPAM-PAAc IPN microgels exhibit an inverse thermo-reversible gelation. Furthermore, IPN microgels undergo the reversible volume phase transitions in response to both pH and temperature changes associated to PAAc and PNIPAM, respectively. Three applications based on this novel hydrogel system are presented: a rich phase diagram that opens a door for fundamental study of phase behavior of colloidal systems, a thermally induced viscosity change, and in situ hydrogel formation for controlled drug release. Clay-polymer hydrogel composites have been synthesized based on PNIPAM gels containing 0.25 to 4 wt% of the expandable smectic clay Na-montmorillonite layered silicates (Na-MLS). For Na-MLS concentrations ranging from 2.0 to 3.2 wt%, the composite gels have larger swelling ratio and stronger mechanical strength than those for a pure PNIPAM. The presence of Na-MLS does not affect the value of the lower critical solution temperature (LCST) of the PNIPAM. Surfactant-free hydroxypropyl cellulose (HPC) microgels have been synthesized in salt solution. In a narrow sodium chloride concentration range from 1.3 to 1.4 M, HPC chains can self-associate into colloidal particles at room temperature. The microgel particles were then obtained in situ by bonding self-associated HPC chains at 23 0C using divinyl sulfone as a cross-linker. The volume phase transition of the resultant HPC microgels has been studied as a function of temperature at various salt concentrations. A theoretical model based on Flory-Huggins free energy consideration has been used to explain the experimental results. Self-association behavior and conformation variation of long chain branched (LCB) poly (2-ethyloxazoline) (PEOx) with a CH3-(CH2)17 (C18) modified surface are investigated using light scattering techniques in various solvents. The polymer critical aggregation concentration (cac) strongly depends on solvent polarity, decreasing as the solvent becomes more hydrophobic.

The finite lifetime of the bound roton pair is included in the theoretical light scattering cross section to explain the shape of the peak in the observed Raman light scattering cross section in He II. A model Hamiltonian is used to describe interactions between quasiparticles for the helium system. The equation of motion for the bound roton pair state, which is taken to be a collective mode of quasiparticle pairs, is solved. The cross section for light scattering is then derived using Fermi's Golden Rule with the bound roton pair as the final state. Since the bound roton pair can decay into two free phonons, a phenomenological width r is included in the cross section. The peak position and shape of the observed cross section are both fitted using a binding energy of εB = 0.37 K for the bound roton pair.