Studies show that dynamical properties of ultra-thin polymer films deviate from those of bulk materials. Despite some controversial issues, there is growing evidence indicating that the interfacial properties play a key role for observed dynamical anomalies. However, how and how much the interfacial properties affect the average dynamics of the nanometer scale systems are still elusive. In this work, we developed several novel techniques to investigate near-free-surface dynamics of thin polymer films. We studied surface dynamics of glassy i-PMMA films using a nano surface hole relaxation technique: a strong substrate property dependence and an unexpected molecular weight dependence were observed; we found that a local Tg of ~40K below bulk Tg could be assigned to the surface region. We used nano gold particle embedding to study PS surface dynamics: enhanced surface dynamics and weak temperature dependence were observed for the surface region; a depth profile with the nm resolution was observed; viscous liquid-like and soft solid-like properties were observed in the first 5.5nm and next 3.3 nm regions in PS films; no molecualr weight dependence was found in glassy PS films. We built a low level noise measurement system to study the thermal polarization noise in PVAc films: cooperative rearranging dynamics were evidenced; the noise power spectral density (PSD) is found to fluctuate around a certain average level without discernable peak shift; we observed some relatively big jumps or fluctuations in successive integrated PSD’s, which indicate some energy exchange between different microscopic domains in glassy polymer systems. We developed a novel nano rheology AFM technique to study the near-free-surface dynamics of thin polymer films: enhanced near-free-surface dynamics with weak temperature dependence are observed for PVAc films, which is similar with the PS case.

Studies show that dynamical properties of ultra-thin polymer films deviate from those of bulk materials. Despite some controversial issues, there is growing evidence indicating that the interfacial properties play a key role for observed dynamical anomalies. However, how and how much the interfacial properties affect the average dynamics of the nanometer scale systems are still elusive. In this work, we developed several novel techniques to investigate near-free-surface dynamics of thin polymer films. We studied surface dynamics of glassy i-PMMA films using a nano surface hole relaxation technique: a strong substrate property dependence and an unexpected molecular weight dependence were observed; we found that a local Tg of ~40K below bulk Tg could be assigned to the surface region. We used nano gold particle embedding to study PS surface dynamics: enhanced surface dynamics and weak temperature dependence were observed for the surface region; a depth profile with the nm resolution was observed; viscous liquid-like and soft solid-like properties were observed in the first 5.5nm and next 3.3 nm regions in PS films; no molecualr weight dependence was found in glassy PS films. We built a low level noise measurement system to study the thermal polarization noise in PVAc films: cooperative rearranging dynamics were evidenced; the noise power spectral density (PSD) is found to fluctuate around a certain average level without discernable peak shift; we observed some relatively big jumps or fluctuations in successive integrated PSD’s, which indicate some energy exchange between different microscopic domains in glassy polymer systems. We developed a novel nano rheology AFM technique to study the near-free-surface dynamics of thin polymer films: enhanced near-free-surface dynamics with weak temperature dependence are observed for PVAc films, which is similar with the PS case.

Using low-temperature (650¢J) Ce3+:YAG doped glass (LTCeYDG) phosphor layer instead of conventional Ce:YAG doped silicone phosphor layer applied to high-power phosphor-converted white-light-emitting diodes (PC-WLEDs) is demonstrated.The glass transition temperature (Tg) of silicone is 150¢J but glass is 750¢J,it shows the glass were employed in high power LED than silicon. The uniformity of phosphor powder doped glass is an important item to discriminates between good and bad. Quantize the uniformity of glass phosphor by image processing software and Distribution Uniformity (Du). Calculate the uniformity of phosphor powder mix with glass powder which has different particle size and measurement optical properties of glass phosphor which has different uniformity. The Du of glass phosphor are 64.46%, 84.65%, 85.24% , 91.85% and the quantum efficiency are 18.49%, 28.31%, 29.73%, 28.56% ,respectively. By using Ceramic tube and low temperature glass powder sintering glass phosphor is a new fabrication. Compare with last fabrication, new fabrication reduce 100¢Jfabrication temperature from 750¢J to 650¢J, 70% material savings and high luminous efficiency. The quantum efficiency and lumen per watt were improved about 7 percentage point from 22.3% to 29.1% and 4.2 lm/W from 36.4 lm/W to 40.68 lm/W. We used the XRD to analyze the glass phosphor of last fabrication and new fabrication and the results show that the higher thermal stress destroys the structure of YAG, lower fabrication temperature used to get higher luminous efficiency.

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The properties of polymers, thin films or bulk, are profoundly influenced by interactions at interfaces with dissimilar materials. Thin, supported, polymer films are subject to interfacial instabilities, due largely to competing intermolecular forces, that cause them to rupture and dewet the substrate. The addition of nanoparticles (such as clay sheets, metallic or semiconductor nanocrystals, carbon nanotubes, etc.) to polymers can substantially affect bulk properties, such as the glass transition and viscosity, and influence the processability of the material. In this dissertation, we contribute to a fundamental understanding of the role of interfacial interactions on both the instabilities exhibited by polymer thin films and the properties displayed by polymer-nanoparticle mixtures. While conditions under which the destabilization of compositionally homogeneous thin films occurs are relatively well understood, the mechanisms of film stabilization in many two-component thin film systems are still unresolved. We demonstrate that the addition of a miscible component to an unstable film can provide an effective means of stabilization. The details of the stabilization mechanism are understood in terms of the compositional dependence of both the macroscopic wetting parameters and the effective interface potential for the system. We find that the suppression of dewetting in the system is not an equilibrium stabilization process and propose a mechanism by which the increased resistance to dewetting may occur. There is also significant interest in understanding the extraordinary property enhancement of polymers that are enabled by the addition of only small concentrations of nanoparticles. If these effects could be distilled down to a few simple rules, they could be exploited in the design of materials for specific applications. In this work, the influence of C60 nanoparticles on the bulk dynamical properties of three polymers is examined. Based on the findings from a range of measurement techniques, including differential scanning calorimetry, dynamic mechanical analysis, dynamic rheology and neutron scattering, we propose that the changes in the glass transition temperature for the polymer-C₆₀ mixtures can be understood in terms of a percolation interpretation of the glass transition. The proposed mechanism is also characterized computationally. / text

Structure and dynamics of nanoconfined glass-forming oligomers and diblock coplymers (BPCs) are investigated by a combination of infrared transition moment orientational analysis (IR-TMOA), positron annihilation lifetime spectroscopy (PALS), grazing incidence small angle X-ray scattering (GISAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and broadband dielectric spectroscopy (BDS). The oligomers probed are the van der Waals type, tris(2-ethyhexyl)phosphate (TEHP) and the self-associating molecules of 2-ethyl-1-hexanol (2E1H). Symmetric and asymmetric poly(styrene-b-1,4-isoprene) P(S-b-I) are studied for the case of BCPs. The samples are confined either in one-dimensional (1D) in form of thin films or in 2D (nanopores) geometrical constraints. The molecular order of TEHP in nanopores as studied by IR-TMOA shows that about 7% of the molecules are preferentially oriented perpendicular to the long axis of the pores due to their interaction with the pore walls. PALS results reveal that 2E1H confined in nanopores exhibit larger free volume with respect to the bulk. In thin films (1D), P(S-b-I) having volume fraction of isoprene blocks f(PI)= 0.55 exhibits randomly oriented lamellae and their thicknesses are directly proportional to the film thickness d(film). For f(PI) = 0.73, perpendicular cylinders with respect to the substrate are observed for d(film)>50 nm but they lie along the substrate plane when d(film) < 50 nm. In AAO pores (2D) with average pore diameter d(pore) of 150 nm, straight nanorods are formed which change to helical structures in 18 nm pores. Molecular dynamics of 2E1H and TEHP constrained in nanopores (2D), is influenced by the interplay between confinement and surface effects. Confinement effects show up as an increase in the structural relaxation rate with decreasing pore sizes at the vicinity of the glass transition temperature. This is attributed to the reduced packing density of the molecules in pores as quantified by PALS results for 2E1H. Whereas the orientation and morphologies of the domains in P(S-b-I) and the chain dynamics of isoprene chains are influenced by the finite--size and dimensionality of confinement, the segmental motion, related to the dynamic glass transition (DGT) of both styrene and isoprene blocks remains unaffected-in its relaxation time-within experimental accuracy. Effects of nanoscale confinement on the molecular dynamics therefore depend on a number of factors: the type of molecules (polymers, low molecular liquids), interfacial interactions and the dimensionality of the constraining geometries.

When a liquid is cooled below its equilibrium freezing temperature, it becomes supercooled and the molecular motions slow down until the system becomes kinetically arrested, forming a glass, at the glass transition temperature. These amorphous materials have the mechanical properties of a solid while retaining the structural properties of a liquid, but do not exhibit the usual features of a thermodynamic phase transition. As such, they present a number of important challenges to our understanding of the dynamics and thermodynamics of condensed phases. For example, supercooled liquids are classified on the basis of the temperature dependence of their transport properties and structural relaxations times. Strong liquids display an Arrhenius behavior, with the logarithm of their viscosity growing linearly with inverse temperature. Fragile liquids behave in a super-Arrhenius manner, where the viscosity appears to diverge at temperatures above absolute zero, suggesting the possibility of an underlying thermodynamic origin to the glass transition. Some complex, network forming liquids, such as water and silica have also been shown to have a dynamical crossover from fragile to strong liquid behavior as the temperature is decreased. The potential energy landscape paradigm, combined with inherent structure formalism, provide a framework for connecting the way particles pack together with the thermodynamics and dynamics of the liquid and glassy phases. However, the complexity of this multi-dimensional surface makes it difficult to fully characterize and rigorous relationships between the nature of particle packing and glass forming properties have not been established. The goal of this thesis is to study some of the general features of glass transition and find the connection between the dynamics and the thermodynamics of glass forming liquids. To this end, the packing landscapes of quasi-one-dimensional hard discs and hard spheres are studied. A two dimensional system of hard discs with diameter σ, confined between two hard walls (lines) of length L, separated by a distance 1<Hd/σ< 1+√(3/4), is studied by using the Transfer Matrix (TM) method and Molecular Dynamics (MD) simulations. The complete packing landscape is characterized in terms of the density distribution of inherent structures and the number of local defect states. It is shown that this model exhibits a dynamic fragile-strong liquid crossover at the maximum in the constant pressure heat capacity (Cp) for the system, similar to that observed in anomalous network forming liquids such as water and silica. Furthermore, we find that rescaling the relaxation times of systems with different channel widths by the relaxation time at the Cp maximum causes all the data to collapse on a single master curve. The Cp maximum occurs at a critical value of the defect concentration. At high defect concentrations, where the defects interact, the fluid is fragile. When the defect concentration is low, relaxation appears to occur through the hopping of isolated defects, leading to Arrhenius dynamics. This suggests the thermodynamics associated with the Cp maximum is intimately related to the dynamic crossover. A system of three-dimensional hard spheres confined in a narrow channel was used to study the effect of a more complicated landscape on the dynamics of the system. For this system, the thermodynamic and dynamic properties of the system were studied for two different channel diameters, the 1<Hd/σ<1+√(3/4) case, which only allows first neighbors contact for the spheres and, 1+√(3/4)< Hd/σ < 1.98, which allows second neighbors contact to exist. For the first case, the TM method was implemented to obtain the thermodynamic properties and MD simulation was used to measure the dynamics. For the case that the second neighbor contact is allowed 1+√(3/4)< Hd/σ < 1.98. The thermodynamic and dynamic properties were obtained using MD simulations. In this channel diameter range, the system creates chiral helical jammed packings and defect states appear where sections of helices with different local chiralities come into contact. The equation of state (EOS) shows the presence of two heat capacity maxima. The high density Cp maximum is linked to fragile strong crossover. Finite size scaling analysis shows that the low density Cp maximum is related to an orientational order transition stabilized by the presence of the defects. This type of transition has been shown to exist in bulk two-dimensional systems but this work is the first study that provides strong evidence of the existence of this transition in a quasi-one-dimensional system in a system with short-range interactions.

The aim of this thesis “Interactions of biodegradable drug carriers with hydrophilic medium” is the study of polymer-hydrophilic medium interactions from the point of view of swelling, erosion and glass transition. In the theoretical part attention was paid to basic information about polyester amides and polyesters with molecule linear, branched, and chain extended. In this part, some basic relations were used, concerning various aspects of biodegradation of polymers, thermal analysis of amorphous phase of polymers and pharmaceutical particulate systems. The main part of the thesis is focused on experiment. Fifteen recently synthesized oligomeric and polymeric carriers were studied in the aspect of their swelling and erosion course. Some of these oligoesters with molecular linear constitution were evaluated during in vitro degradation process via glass transition tested by DSC method measurements. No correlation signs between swelling kinetics and glass transition temperature values course were found. These two molecular relaxation parameters are the manifestations of different mechanism. Swelling extent is influenced by osmotic phenomena, whilst glass transitions by molecule polarization effects. This work is one of the first steps examining these drug carriers. The results of this work will be used in choosing perspective drug carriers and in further researches. / Šio darbo „Biodegraduojančių vaistų nešėjų sąveika su hidrofiline terpe“ tikslas ištirti polimero bei hidrofilinės terpės sąveiką atsižvelgiant į brinkimą, eroziją bei stiklėjimo temperatūros pokyčius, galimą ryšį tarp polimero brinkimo ir stiklėjimo temperatūros, apžvelgti nano ir mikro dalelių paruošimo bei įvertinimo teoriją. Literatūros apžvalgoje dėmesys skiriamas informacijai apie poliesteramidus ir linijinius, šakotus ar praplėstos grandinės poliesterius. Šioje dalyje aptariami įvairūs polimerų biodegradacijos, amorfinės fazės polimerų terminės analizės aspektai, taip pat nano bei mikrodalelės kaip vaisto forma. Pagrindiniai darbo uždaviniai yra ištirti penkiolika neseniai susintetintų oligomerinių bei polimerinių vaistų nešėjų atsižvelgiant į jų brinkimą bei eroziją, įvertinti kai kurių linijinių oligoesterių degradacija in vitro atsižvelgiant į stiklėjimo temperatūrą matuojant diferencinės skenuojančios kalorimetrijos metodu. Atkreiptas dėmesys į galimą ryšį tarp stiklėjimo temperatūros ir brinkimo kinetikos, kurio nepastebėta; manoma, kad dėl to, jog molekulės grandinės atsipalaidavimas pasireiškia dėl skirtingų mechanizmų. Brinkimo laipsnis priklauso nuo osmotinių reiškinių, o stiklėjimo temperatūrai įtaką daro molekulės poliarizacija. Šis darbas yra pradinis etapas tiriant šiuos polimerus. Šio darbo rezultatai padės atrenkant perspektyvias medžiagas tolimesniems tyrimams, prognozuojant galimas jų panaudojimo galimybes.

This thesis reports on a comprehensive experimental study of the collective dynamics of colloidal hard sphere suspensions. The main quantity measured is the coherent Intermediate Scattering Function (ISF) using a range of techniques based on Dynamic Light Scattering (DLS). The collective dynamics are measured as a function of scattering vector for volume fractions spanning from dilute samples, through the fluid phase and the metastable region, up until deep in the glass region. This work describes two major explorations: (i) the effect of volume of fraction on the q-dependency of the collective dynamics; and (ii) a study of the ageing processes in colloidal glasses. The present work is unique in the application of several advanced experimental techniques, and in the level of averaging that has been carried out, enabling a more sophisticated analysis than has previously been possible. This includes the characterization of non-Fickian processes and the determinatio n of the current-current correlation function (CCCF) in the metastable fluid, and the quantitative characterization of the ageing process in the hard sphere glass. In addition, by combining aspects of the coherent and incoherent ISFs, this work also allows the expression of the collective dynamics in terms of the single particle displacement. The results show a dynamical change at the freezing point (f), which exposes the incapacity of the system to dissipate thermal energy via diffusing momentum currents, i.e. viscous flow. The structural impediments responsible for this, associated with dynamical heterogeneities, begin at the structure factor peak, and spread to other spatial modes as the volume fraction increases. Above the glass transition (g), structural relaxation becomes arrested at all spatial modes probed, i.e. flow is arrested. It is found that, following the quench, samples above the glass volume fraction approach some final

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.