Detailed-atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials

Diffusion of Water in Amorphous Polymers at Different Temperatures Using Molecular Dynamics Simulation

“…A "cut off' distance (define the distance that the algorithm checks the non-bond interactions of the atoms) of 9,5A was assigned were generally should not be longer than the half size of the cell for consistency with the image convention, which means that the van der Waals and electrostatic interactions are considered zero for interatomic distances greater than the cut-off distance [44]. Ten different configurations of the cell were generated in order to collect various statistical data for the diffusion coefficient, generated from 0,1 to 1,1 g/cm3 in order to avoid spin catenations ( rings within the cell which during the construction of the structure are merged within another) [21]. After the production of the cells each structure was minimised were at this stage the algorithm seeks the local minimum of the potential energy.…”

“…After the production of the cells each structure was minimised were at this stage the algorithm seeks the local minimum of the potential energy. Then the equilibration procedure takes place in order to achieve a uniform representation of the microstructures and avoid continuum-holes (gaps within the structure which continue to infinity because of the employment of PBC) which would affect the calculation of the diffusivity [21]. At this stage the NVT ensemble was used were the number of atoms, the volume and the temperature was controlled.…”

“…All the above were correlated and examined in order to signify from the chemical changes the changes of the structural properties, not being able though to gain knowledge from the bulk of the material from a nano-simulation tool [9][10][11][12][13][14][15][16][17][18][19][20]. On the other hand Molecular modelling in particular Molecular Dynamics (MD) which represents the material in a molecular base by applying various thermodynamic constraints (density-volume, temperature, pressure etc) and empirical potential functions has been able to demonstrate the diffusion mechanism of water in terms of numerical application, calculate the diffusion coefficient [21][22][23][24][25][26] and identify surface or composition of the materials and component dependence on the adhesion failure without though achieving an extensive experimental studying [27][28][29].…”

“…In nanoscale and based on Brownian motion with the aid of Einstein's relationship the self-diffusion coefficient of the penetrant molecule in three dimensions can be evaluated from the limiting slope of the mean square displacement as a function of time [21,39]: Where Na is the number of atoms following with the aid of the simulation their trajectories, ri the position vector of atom a and the MSD is the averaged mean squared displacement over the number of atoms-water molecules in the polymer matrix. The diffusion coefficient can be derived by averaging all the averaged MSD of water molecules versus Time of different polymer configurations in order to select various statistical data.…”

Simulation of Volumetric Swelling of Degradable Poly[(Rac-Lactide)-Co-Glycolide] Based Polyesterurethanes Containing Different Urethane-Linkers

“…Furthermore, detailed atomistic molecular modeling approaches have been utilized for investigation of transport phenomena of small penetrants such as water inside amorphous polymers by simulation. Most of these efforts were focused on achieving better insights into the relationships of structural and molecular features of polymeric systems and transport properties such as free volume distribution of the samples and the mobility of backbone atoms (19). Following these experiences, fundamental parameters involved in degradation of poly(α-hydroxy esters), especially the uptake of water molecules and the hydrolysis of ester oligomers have been studied by atomistic simulation and quantum chemical methods (4,20,21).…”