Self-diffusion and Cooperative Diffusion in Semidilute Polymer Solutions as measured by Fluorescence Correlation Spectroscopy

We present a comprehensive investigation of polymer diffusion in the semidilute regime by fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS). Using single-labeled polystyrene chains, FCS leads to the self-diffusion coefficient while DLS gives the cooperative diffusion coefficient for exactly the same molecular weights and concentrations. Using FCS we observe a new fast mode in the semidilute entangled concentration regime beyond the slower mode which is due to self-diffusion. Comparison of FCS data with data obtained by DLS on the same polymers shows that the second mode observed in FCS is identical to the cooperative diffusion coefficient measured with DLS. An in-depth analysis and a comparison with current theoretical models demonstrates that the new cooperative mode observed in FCS is due to the effective long-range interaction of the chains through the transient entanglement network

Study of surface changes on industrial glasses with AFM, FE-SEM, EDX, SNMS and LM : Part 2. Surface changes by water drop etching, annealing at atmosphere and flame treatment

One of the possible defects in sputter coating layers are cone shaped rods which originate from the float glass surface on the atmosphere side. The glass surface had been etched by wax-like corrosion droplets and holes were formed into the glass skin after washing. This results in inhomogeneity on the surface, which induces an inhomogenous deposition pattern of the material on the surface during the process of sputtering. In contrast, the tin bath side is shown to be an ideal coating surface without any inhomogen eity. In some eases however, it could not be bent above the glass transition temperature (Tg) in air due to formation of bloom patterns, which make the glass milky. Our studies revealed that phase separation is the ultimate cause of the observed bloom formation. In addition, sulphur flakes and needle-like nanocrystallites were detected on the tin bath side as well as hexagonal nanocrystallites on the atmosphere side of the annealed float glass. It was also found that flame treatment of borosilieate and lead crystal glasses induced two changes on the glass surfaces. These are precipitation of evaporation products and phase separation beneath the glass skin. The samples were studied by a combination of field emission scanning electron microscopy (FE-SEM) with different accelerating voltages and atomic force microscopy (AFM)

Study of surface changes on industrial glasses with AFM, FE-SEM, EDX, SNMS and LM : Part 1. Glass skin and corrosion

By combining different analytieal techniques, including modern high resolution imaging tools such as field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), new phenomena in the surface, near surface and bulk structure of various industrial glasses (without any cleaning process) have been diseovered. Investigations of soda-lime-silica container glass and lead silicate glass tubings exposed to atmospheric and to dried air are presented. The results of the first part of this paper can be explained with an SiO2 rich skin on the glass, which can protect the glass against the attack of external media. If the skin was mechanically injured, inhomogeneous corrosion products on pm scale grew around the injured site after exposure to humid air for times between days up to one year. Microchannels were formed through the injured site due to restricted ion exchange, followed by a local increase of the pH value and consequently the dissolution of the glass network. Finally some stress in the glass, yielded during manufacture, can be partially released and the cutting behaviour is improved. Faster cooling results in a thinner skin and the ions in the glass are able to migrate to the surface more easily when surrounded by some reactive media. Slower cooling results in thicker skin and wax-like droplets instead of erystallites are formed on the surface at a later stage in humid air. The wax-like droplets can etch the glass skin locally, followed by the growth of inhomogeneous corrosion products similar to the injury induced corrosion. If the fresh glass surface was hot-end treated, the quality of the adjacent coating layer depended strongly on the thickness of the skin

Scanning probe microscopy with 'chemical sensitivity'

We discuss recent developments in scanning probe microscopy aiming to combine ultra-high lateral resolution with the potential of “chemical sensitivity”. Particular attention is given to techniques beyond the well-established scanning tunneling microscopy (STM) and atomic force microscopy (AFM), which allow surface imaging with atomic resolution, however, do hardly allow chemical identification of the structures under study. Starting with “nanomechanical” imaging using a modified AFM capable of local friction and elasticity measurements, we demonstrate that scanning probe microscopy can well be combined with a kind of materials recognition capability. We then turn to scanning near-field optical microscopy and spectroscopy (SNOM), a technique that combines high lateral resolution with nearly all the information accessible by optical techniques. In both cases, the present spatial resolution limits are discussed

Dewetting at the interface between two immiscible polymers

We review the recent theoretical and experimental efforts that have been made in studying the dynamics of dewetting at the interface between two liquids. While detailed theoretical predictions are already available, the experimental studies are still at an early stage. The first experiments using high-molecular-weight homopolymers not only enable a study of the dewetting dynamics to be made, but also allow a detailed analysis of the deformed liquid/liquid interface around the growing holes to be undertaken. The experimental results are compared with theoretical predictions

Wetting at polymer surfaces and interfaces

Experimental research on wetting in polymer films is a subject that is reaching maturity. We review progress from the past few years in research into the influence of a boundary in polymer blends, concentrating largely on the wetting transition, and the growth of wetting layers, where we pay particular attention to blends in which hydrodynamic flow plays a dominant role. A summary of work over the same period concerning the dewetting of polymer films is also included, along with a discussion of the role of pattern formation caused by dewetting and topographically and chemically patterned substrates. We conclude by summarising some experiments that we believe may inspire future research