ترغب بنشر مسار تعليمي؟ اضغط هنا

Entanglement reduction induced by geometrical confinement in polymer thin films

112   0   0.0 ( 0 )
 نشر من قبل Nicolas Ariel Garcia
 تاريخ النشر 2018
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We report simulation results on melts of entangled linear polymers confined in a free-standing thin film. We study how the geometric constraints imposed by the confinement alter the entanglement state of the system compared to the equivalent bulk system using various observables. We find that the confinement compresses the chain conformation uniaxially, decreasing the volume pervaded by the chain, which in turn reduces the number of the accessible inter-chain contact that could lead to entanglements. This local and non-uniform effect depends on the position of the chain within the film. We also test a recently presented theory that predicts how the number of entanglements decreases with geometrical confinement.



قيم البحث

اقرأ أيضاً

Structure of polymer electrolytes membranes, e.g., Nafion, inside fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ul tra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films and, in turn, on transport properties, has not been sufficiently explored yet. Here, we report about classical Molecular Dynamics simulations of hydrated Nafion thin-films in contact with unstructured supports, characterized by their global wetting properties only. We have investigated structure and transport in different regions of the film and found evidences of strongly heterogeneous behavior. We speculate about the implications of our work on experimental and technological activity.
In both research and industrial settings spin coating is extensively used to prepare highly uniform thin polymer films. However, under certain conditions, spin coating results in films with non-uniform surface morphologies. Although the spin coating process has been extensively studied, the origin of these morphologies is not fully understood and the formation of non-uniform spincast films remains a practical problem. Here we report on experiments demonstrating that the formation of surface instabilities during spin coating is dependent on temperature. Our results suggest that non-uniform spincast films form as a result of the Marangoni effect, which describes flow due to surface tension gradients. We find that both the wavelength and amplitude of the pattern increase with temperature. Finally, and most important from a practical viewpoint, the non-uniformities in the film thickness can be entirely avoided simply by lowering the spin coating temperature.
We employ 3D Langevin Dynamics simulations to study the dynamics of polymer chains translocating through a nanopore in presence of asymmetric solvent conditions. Initially a large fraction ($>$ 50%) of the chain is placed at the textit{cis} side in a good solvent while the $trans$ segments are placed in a bad solvent that causes the chain to collapse and promotes translocation from the $cis$ to the $trans$ side. In particular, we study the ratcheting effect of a globule formed at the textit{trans} side created by the translocated segment, and how this ratchet drives the system towards faster translocation. Unlike in the case of unbiased or externally forced translocation where the mean first passage time $langle tau rangle $ is often characterized by algebraic scaling as a function of the chain length $N$ with a single scaling exponent $alpha$, and the histogram of the mean first passage time $P(tau/langletau rangle)$ exhibits scaling, we find that scaling is not well obeyed. For relatively long chains we find $langle tau rangle sim N^alpha$ where $alpha approx 1$ for $varepsilon/k_{B}T > 1$. In this limit, we also find that translocation proceeds with a nearly constant velocity of the individual beads(monomers), which is attributed to the coiling of the globule. We provide an approximate theory assuming rotat ional motion restricted on a 2D disc to demonstrate that there is a crossover from diffusive behavior of the center of mass for short chains to a single file translocation for long chains, where the average translocation time scales linearly with the chain length $N$.
In this study, thin elastic films supported on a rigid substrate are brought into contact with a spherical glass indenter. Upon contact, adhesive fingers emerge at the periphery of the contact patch with a characteristic wavelength. Elastic films are also pre-strained along one axis before initiation of contact, causing the fingering pattern to become anisotropic and align with the axis along which the strain was applied. This transition from isotropic to anisotropic patterning is characterized quantitatively and a simple model is developed to understand the origin of the anisotropy.
114 - B. X. Wu , K. Jin , J. Yuan 2009
A series of electron-doped cuprate La(2-x)CexCuO4 thin films with different thicknesses have been fabricated and their annealing time are adjusted carefully to ensure the highest superconducting transition temperature. The transport measurements indi cate that, with the increase of the film thickness (<100 nm), the residual resistivity increases and the Hall coefficient shifts in the negative direction. Further more, the X-ray diffraction data reveal that the c-axis lattice constant c0 increases with the decrease of film thickness. These abnormal phenomena can be attributed to the insufficient oxygen reduction in the thin films. Considering the lattice mismatching in the ab-plane between the SrTiO3 substrates and the films, the compressive stress from the substrates may be responsible for the more difficult reduction of the oxygen in the thin films.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا