A recently developed method was employed to study the deposition of colloidal particles under well-controlled hydrodynamic conditions. With this technique we studied the effects of polymers on the impingement of colloidal particles onto flat surfaces. In the deposition-detachment studies of bare latex particles, anomalous deposition rates and surface motions were observed. These types of behavior can be qualitatively explained by surface protrusions on the latex surface. Bare particles were dislodged from the surface by hydrodynamic forces exerted on them and by surface collisions between freely suspended and deposited particles. By coating the particles with neutral polymer, we found a decrease in the deposition rate but an increase in adhesion. The presence of free polymer in the jet increases the probability of escape. The detachment rate can be explained by an exchange between polymer segments bridging the particles to the surface and those freely dissolved in the jet. The presence of cationic polyelectrolyte promotes deposition and prevents the release of the particles.

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No description available.

The nonlinear visoelastic behavior that accompanies large transient deformations in high molecular weight polymer melts and concentrated solutions is not at all well-understood, because equipment suitable for the investigation of such phenomena have not been available. This lack of understanding has limited the advancement of plastics processing technology, because the deformations that occur in polymer processing often take the melt well into the nonlinear regime. Furthermore, it has not been possible to test constitutive equations formulated to describe nonlinear phenomena. / A new rheometer, equipped with a specially designed shear stress transducer, has been developed to examine the nonlinear viscoelastic behavior of polymeric liquids. Deformations that can be generated include interrupted shear and large amplitude oscillatory shear. Using the new instrument, a thorough study was made of the rheological behavior of polyisobutylene at 22(DEGREES)C. The results obtained from these experiments were used to evaluate the predictive ability of a constitutive equation recently proposed by Mewis and De Cleyn.

Leung, Chung Yin = 聚合物濃度對湍流減阻的影響 / 梁頌賢. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 106-108). / Abstracts in English and Chinese. / Leung, Chung Yin = Ju he wu nong du dui tuan liu jian zu de ying xiang / Liang Songxian. / Abstract --- p.i / 概要 --- p.iii / Acknowledgements --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The phenomenon of polymer drag reduction --- p.1 / Chapter 1.2 --- The Phenomenology of drag reduction --- p.9 / Chapter 1.3 --- A recent theory --- p.19 / Chapter 2 --- Review of a recent theory of drag reduction --- p.21 / Chapter 2.1 --- The balance equations --- p.21 / Chapter 2.2 --- Estimating the average terms --- p.26 / Chapter 2.2.1 --- Average terms for flexible polymers --- p.27 / Chapter 2.2.2 --- Average terms for rodlike polymers --- p.32 / Chapter 2.3 --- Solving the balance equations --- p.34 / Chapter 3 --- Behavior near the maximum drag reduction asymptote --- p.42 / Chapter 4 --- Reduction of drag at small concentrations --- p.57 / Chapter 5 --- Velocity profiles and friction factor relations --- p.61 / Chapter 5.1 --- Newtonian flow without polymer --- p.61 / Chapter 5.2 --- Flow at high polymer concentration --- p.63 / Chapter 5.3 --- Flow at intermediate concentration --- p.68 / Chapter 6 --- The Reynolds stress profile --- p.88 / Chapter 7 --- Percentage drag reduction --- p.95 / Chapter 8 --- Conclusion and future work --- p.104 / Bibliography --- p.106

Dilute solution properties of three difficult-to-analyze macromolecular systems were investigated and clarified. Two were notorious for having highly time-in-solution dependent properties, nitrocellulose and lignin, while the third was an ideal model branched methacrylate polymer with which to examine unanswered questions in polymer hydrodynamic behavior. Gel permeation chromatography with a differential viscosity detector (GPC/DV) was employed to study the dilute solution properties of various polymers, specifically their absolute molecular weight distributions and hydrodynamic behavior. The study was divided into three parts. The first part focused on the time dependent change in molecular weight of nitrocellulose. Samples having 12.58% and 13.5% levels of nitration were investigated in THF and EtOAc. GPC/DV, LALLS, FT-IR and intrinsic viscosity experiments revealed that the materials existed as associated molecules in solution which decreased in molecular weight upon storage to extents dependent on the solvent. The second part was an examination of the hydrodynamic behavior of hydroxypropylated lignins using GPC/LALLS/DV and VPO. These materials were found to increase in molecular weight upon storage in solution due to association. Special precautions had to be taken in running experiments to obtain the correct molecular weights and molecular weight distributions. The last part involved a fundamental study of PMMA-g-PMMA's having similar molecular weights but containing different levels of branching. Variable temperature GPC/LALLS/DV was employed to obtain molecular weight distributions, branching parameters, average chain dimensions and information on the hydrodynamic behavior of these branched systems. Samples containing up to 40% of long chain branching were found to obey the universal calibration analytic scheme of GPC. / Ph. D.

The generalized Langevin equation (GLE) has been used to describe the dynamics of particles in a stationary environment. To better understand the dynamics of polymerization, the GLE has been generalized to the irreversible generalized Langevin equation (iGLE) so as to incorporate the non-stationary response of the solvent. This non-stationary response is manifested in the friction kernel and the behavior of the projected (stochastic) force. A particular polymerizing system, such as living polymerization, is specified both through the parameters of the friction kernel and the potential of mean force (PMF). Equilibrium properties such as extent of polymerization have been obtained and are consistent with Flory-Huggin¡¯s theory. In addition, time-dependent non-equilibrium observables such as polymer length, the polymer length distribution, and polydispersity index (PDI) of living polymerization have been obtained. These have been compared to several experiments so as to validate the models, and to provide additional insight into the thermodynamic and kinetic properties of these systems. In addition to the iGLE, a stochastic model has been used to study the effect of nonequilibrium reactivity on living polymerization. This model can be used to determine whether the reaction is controlled by kinetics or diffusion. A combination of the iGLE and stochastic models may help us obtain more information about living polymerization.

A slit die has been constructed to use both flow birefringence and direct pressure measurements to study the extrapolated exit pressure (Px) and the exit pressure theory used to evaluate the magnitude of the primary normal stress difference (N1) from the value of the exit pressure. Flow birefringence is used to directly assess the principal assumptions in the exit pressure theory and to evaluate the magnitude of Px from an expression derived from the macroscopic momentum balance equation. The effect of stress field rearrangement upstream of the die exit plane on the value of the exit pressure was then evaluated using flow birefringence data. The effect of stress field rearrangement was also shown to affect the pressure drop ΔP/ΔL in the exit region of the die and the pressure distribution from the centerline of the slit to the die wall. To complement the experimental investigation, a mixed penalty method finite element simulation of the die swell problem was performed using the White-Metzner and upper-convected Maxwell constitutive equations. The flow birefringence experiments were performed for a polystyrene (Styron 678), LDPE (NPE 952), and HDPE (LY600-00) melts for the following shear rate (γ̇) and wall shear stress (σw) 0.05 ≤ γ̇w ≤ 3.2 s⁻¹ and 4.84 ≤ σw ≤ 16.4 KPa. It was found that the flow in the die exit region is not a unidirectional shear flow, which is direct violation of the assumptions in the exit pressure theory. Normal stresses generated by an elongational flow field were observed along the slit centerline and in the region adjacent to the die walls. Also, shear stress contributions due to stress field rearrangement evaluated using an expression obtained from a macroscopic momentum balance, comprise over 50% of the magnitude of the calculated exit pressure. The numerically calculated stress field was in good agreement with the results of the flow birefringence results. Convergence for the numerical technique was limited to Deborah numbers of 0.61 for the White-Metzner model and 0.75 for the upper-convected Maxwell constitutive equation. / Ph. D.

While theoretical treatments of liquid spreading on solid surfaces can be found in abundance in the literature, relatively few experimental studies have been performed. This study focused on the experimental detection of polydimethylsiloxane spreading on polymer surfaces in the spreading regime where gravitational and inertial forces are negligible. The techniques of x-ray photoelectron spectroscopy (XPS), reflection absorption spectroscopy (RAS), and contact angle analysis were used to investigate this problem. XPS analysis indicated that the surface spreading or "creeping" was very slow, moving only several centimeters per several hundred hours in some cases. An interesting observation was that the spreading film seemed to reach a "steady state" concentration when covering an area. Similar results were seen for both horizontal and vertical substrate surfaces with XPS, and there seemed to be a substrate dependence. Angular-dependent XPS analysis revealed that the film was very thin (<20A) and not a complete layer. Contact angle analysis was used to monitor the siloxane movement, although there was a contact angle dependence on x-ray exposure time, indicating cross-linking of the surface film. Contact angle variations were also used to show that the film characteristics may be dependent on the nature of the polymer substrate. Reflection absorption spectroscopy was used to investigate thin substrate polymer films, and it was shown that theoretical predictions of absorption band intensity correlated reasonably well with the experiment. This technique was also used to investigate the surface siloxane layer and indicated that under some conditions, the orientation of the surface silicone layer may be occurring. / M.S.

Chemically identical but topologically different cyclic and linear polymers not only result in marked differences in dynamics, but also lead to unique transport properties of their blends, where cyclic polymers have chances to be threaded onto the linear polymers. This dissertation addresses the effect of ring architecture on dynamics using different time/length scale techniques: self-diffusion coefficients, NMR spin-spin relaxation time (T2) and bulk viscosity. In deuterated water, synthesized cyclic poly(oxyethylene) (CPOE) (400-1500 g/mol) diffused faster than corresponding linear POE (LPOE) and linear POE dimethyl ether (LPOEDE). However, the self-diffusion coefficients in melts were arranged in the following manner: LPOEDE > CPOE > LPOE, in excellent agreement with T2 and viscosity data, showing topological and chain end effects. Compared to LPOEDE, both CPOE and LPOE had higher activation energies for viscosity with less dependence on the molecular weight. In the blends of CPOE and LPOE for 900 and 1500 g/mol, the diffusion coefficient and viscosity in melts were higher and lower than the values predicted by a binary mixing rule, respectively. These deviations were attributed to the threading conformation, and the weight fraction of the threaded chains for 1500 g/mol was estimated by a three-term mixing rule. This threading conformation also appeared to influence such important bulk properties as the glass transition and spherulitic growth rate of the blends.