Phase behaviour of block copolymer melts with arbitrary architecture

The Leibler theory [L. Leibler, Macromolecules, v.13, 1602 (1980)] for microphase separation in AB block copolymer melts is generalized for systems with arbitrary topology of molecules. A diagrammatic technique for calculation of the monomeric correlation functions is developed. The free energies of various mesophases are calculated within the second-harmonic approximation. Model highly-branched tree-like structures are considered as an example and their phase diagrams are obtained. The topology of molecules is found to influence the spinodal temperature and asymmetry of the phase diagrams, but not the types of phases and their order. We suggest that all model AB block-copolymer systems will exhibit the typical phase behaviour.Comment: Submitted to J. Chem. Phys., see also http://rugmd4.chem.rug.nl/~morozov/research.htm

Can a Protein Adsorb on its Own? The Thermodynamics of Ion Participation

We present a general thermodynamic method to obtain information about co-adsorption and oo-partitioniiug of low molecular weight ions upon adsorption or partitioning of proteins between two phases. Esin-Markov coefficients are central quantities. By this procedure useful additional information is obtained that, in turn, can be used in mechanistic interpretations. Applications are presented for (1) ion binding to free BSA, (2) charge adjustments in the protein and on the surface upon adsorption of BSA on silver iodide and (3) ion co-participation upon solubilization of cytoohrome-C into micro-emulsdon .droplets

Dynamic density functional theory for microphase separation kinetics of block copolymer melts

In this paper, we describe a numerical method for the calculation of collective diffusion relaxation mechanisms in quenched block copolymer melts. The method entails the repeated calculation of two opposing fields-an external potential field U, conjugate to the density field rho, and an energetic interaction field E. The external field is calculated by numerical inversion of the density functionals and the energetic interaction field is calculated directly by integration over the density field. When the two fields are balanced U = E, we recover the self-consistent field solutions; when the two fields are off balance, the spatial gradient of E-U is the thermodynamic force which drives the collective diffusion. We introduce a simple local coupling approximation for the Onsager kinetic coefficients of short freely jointed chains in weakly ordered systems. Fluctuations are added by incorporation of a random Langevin force in the diffusion equation. Numerical results of decomposition in symmetric and asymmetric diblock copolymer melts indicate that the method is capable of describing extremely slow defect annihilation relaxation modes. We find that in the nonlinear regime, the density patterns evolve to metastable states, in which isolated defects separate relatively well-ordered crystalline microdomains. These final states are typical for many industrial applications of incompletely relaxed copolymer melts

Application of free energy expansions to mesoscopic dynamics of copolymer melts using a Gaussian chain molecular model

The present paper deals with some mathematical aspects of generalized time-dependent Ginzburg-Landau theories for the numerical simulation of mesoscale phase separation kinetics of copolymer melts. We shortly discuss the underlying theory and introduce an expansion of the external potential, to be used in the dynamics algorithm, which is similar to free-energy expansions. This expansion is valid for both compressible and incompressible multicomponent copolymer melts using a Gaussian chain model. The expansion is similar to the well-known random phase approximation (RPA) but differs in some important aspects. Also, the application of RPA like free energy expansions to dynamics is new. Our derivation leads to simple expressions for the vertex coefficients, which enables us to numerically calculate their full wave Vector dependence, without assuming an ordered morphology. We find that our fourth-order vertex is negative for some wave vectors which has important consequences for the simulation of mesoscopic dynamics. We propose a fitting procedure for the vertex coefficients to overcome the computationally expensive calculation of the linear and bilinear expansion terms in the expansion, This procedure provides analytically derived parameters for a gradient free energy expansion, which allows for a whole new class of phase-separation models to be defined. (C) 1997 American Institute of Physics

The possible role of matrix metalloproteinase (MMP)-2 and MMP-9 in cancer, e.g. acute leukemia

In the past decades, a lot of effort has been put in identifying the role of matrix metalloproteinases (MMPs) in cancer. The main role of MMPs in angiogenesis, tumor growth and metastasis is degradation of extracellular matrix (ECM) and release and/or activation of growth factors through their degradative activity. The degradative activity finally results in cancer progression. MMP-inhibitors (MMPIs) have already been designed and tested, based on the degradative role of MMPs in cancer progression. First clinical trials with MMPIs have been performed with disappointing results, showing that in order to use MMP-inhibition the mechanisms underlying MMP-expression in cancer have to be further elucidated. This paper reviews the mechanisms of MMPs on molecular and cellular level and discusses the role for MMPs and MMP-inhibition in cancer with special focus on acute leukemia

Orientational phase transitions in the hexagonal phase of a diblock copolymer melt under shear flow

We generalize the earlier theory by Fredrickson [J. Rheol. v.38, 1045 (1994)] to study the orientational behaviour of the hexagonal phase of diblock copolymer melt subjected to steady shear flow. We use symmetry arguments to show that the orientational ordering in the hexagonal phase is a much weaker effect than in the lamellae. We predict the parallel orientation to be stable at low and the perpendicular orientation at high shear rates. Our analysis reproduces the experimental results by Tepe et al. [Macromolecules v.28, 3008 (1995)] and explains the difficulties in experimental observation of the different orientations in the hexagonal phase.Comment: 21 pages, 6 eps figures, submitted to Physical Review

Orientations of the lamellar phase of block copolymer melts under oscillatory shear flow

We develop a theory to describe the reorientation phenomena in the lamellar phase of block copolymer melt under reciprocating shear flow. We show that similar to the steady-shear, the oscillating flow anisotropically suppresses fluctuations and gives rise to the parallel-perpendicular orientation transition. The experimentally observed high-frequency reverse transition is explained in terms of interaction between the melt and the shear-cell walls.Comment: RevTex, 3 pages, 1 figure, submitted to PR

The one health problem of azole resistance in Aspergillus fumigatus: current insights and future research agenda

Azole resistance is a concern for the management of diseases caused by Aspergillus fumigatus in humans. Azole fungicide use in the environment has been identified as a possible cause for development of resistance, which increases the complexity and number of stakeholders involved in this emerging problem. A workshop was held in Amsterdam early 2019 in which stakeholders, including medical and agricultural researchers, representatives from the government, public health, fungicide producers and end-users, reviewed the current evidence supporting environmental selection for resistance and to discuss which research and measures are needed to retain the effectiveness of the azole class for environmental and medical applications. This paper provides an overview of the latest insights and understanding of azole resistance development in the clinical setting and the wider environment. A One Health problem approach was undertaken to list and prioritize which research will be needed to provide missing evidence and to enable preventive intervention