Juan Manuel Castillo Sánchez

Wissenschaftlicher Mitarbeiter

Dr. M.Sc. Juan Manuel Castillo Sánchez

FB Maschinenbau und Verfahrenstechnik
Lehrstuhl für Thermodynamik
Technische Universität Kaiserslautern
Erwin-Schrödinger-Straße 44
Gebäude 44/556
67663 Kaiserslautern

Tel.: +49(0)631 205-5586
Fax: +49(0)631 205-3835

E-Mail: juan-manuel.castillo[at]mv.uni-kl.de

Projektbeschreibung

  • Molecular simulation of hydrogels

The conformation transition of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel as a function of the methanol mole fraction in water/methanol mixtures, and of the concentration of different salts, is studied by atomistic molecular dynamics simulation with explicit solvents. Our objective is developing a force field that can reproduce the experimental conformation transition of the hydrogel with changes in the temperature. In this way we will be able to identify the different factors that influence the dynamics of the hydrogel, which is vital to fully exploit its potential in drug delivery systems, tissue engineering, micro actuators, and many other applications.

 

Collapse of a PNIPAAm chain in a water/methanol mixture with 0.1 mol/mol-1 methanol at 298 K and 1 bar. The color surface shows the local concentration of the hydration shell, water in blue and methanol in red.

Video 1: water solution

Simulation of one single PNIPAAm chain in water solution, showing the structure of the polymer and the water-polymer hydrogen bonds. The atoms of the central monomers are represented explicitly, while for the rest of the monomers only the backbone is drawn.

<iframe class="youtube-player" type="text/html" src="http://www.youtube.com/embed/VIDEO_ID" frameborder="0" height="385" width="640"> </iframe>

Video 2: water/methanol solution

Simulation of one single PNIPAAm chain in a water/methanol solution (methanol concentration equal to 0.1 mol/mol), showing the structure of the polymer and the solvent-polymer hydrogen bonds. The atoms of the central monomers are represented explicitly, while for the rest of the monomers only the backbone is drawn.

<iframe class="youtube-player" type="text/html" src="http://www.youtube.com/embed/VIDEO_ID" frameborder="0" height="385" width="640"> </iframe>

Video 3: methanol solution

Simulation of one single PNIPAAm chain in methanol solution, showing the structure of the polymer and the methanol-polymer hydrogen bonds. The atoms of the central monomers are represented explicitly, while for the rest of the monomers only the backbone is drawn.

<iframe class="youtube-player" type="text/html" src="http://www.youtube.com/embed/VIDEO_ID" frameborder="0" height="385" width="640"> </iframe>

Video 4: cononsolvency

Simulation of one single PNIPAAm chain in a water/methanol solution (methanol concentration equal to 0.1 mol/mol), showing the local concentration of the solvents around the PNIPAAm chain in the cononsolvency region. Water is painted in blue, and methanol in red. While the polymer is soluble in pure water and pure methanol at low temperatures, in water/methanol solutions the polymer abandons its coiled structure and collapses. 

<iframe class="youtube-player" type="text/html" src="http://www.youtube.com/embed/VIDEO_ID" frameborder="0" height="385" width="640"> </iframe>

Projektbeschreibung

  • Molecular simulation of Self-Assembled Monolayers

Self-assembled monolayers of silane molecules are widely used to modify and functionalize surfaces. In particular, the use of silicon wafers as a substrate is a common model system because of the highly controllable properties of this material. By choosing the end group of the silane, the surface wettability can be tuned. At the same time, the resulting monolayers are mechanically robust and thermally stable up to at least 250 °C. After silanization, the silicon wafer can be easily cleaned and handled in different applications, like adsorption of proteins or bacteria, polymer dewetting, or selective area atomic deposition.

a) Arrangement of the superficial oxygen atoms of beta-cristobalite (101). The minimum oxygen-oxygen distance is ~0.44 nm. The oxygen atoms can either be bonded to an alkylsilane molecule (black circles), or not (gray circles). b) Arrangement of alkylsilane molecules, represented as rigid sticks. The black lines indicate the orientation of the molecules with respect to the molecular axis. Both figures were obtained from a MD simulation of DTS molecules at 4.5 nm^(-2) coverage, 280 K, and 1 bar.

We aim to complement the experimental characterization of dodecyltrichlorosilane and octadecyltrichlorosilane monolayers on silica by the use of molecular dynamics simulations at ambient conditions and a wide range of coverage. It is found that the tilt angle and the relative layer thickness depend only on a function of coverage, and not on alkylsilane chain length. Other properties such as the gauche factor or the surface roughness do depend on chain length, as the inter chain interaction is the most important interaction in the system. The most decisive factor for monolayer stability is the horizontal ordering of the alkylsilane chains.

Tilt angle (angle of the alkylsilane molecules with the normal to the surface) as a function of coverage, obtained by molecular simulation. Squares, DTS; triangles, OTS; line, quadratic fit. Experimental (open symbols) and other simulation (closed symbols) data for OTS are also represented.


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Ausbildung

09/1991 - 07/1995

Julio-Rodriguez-Gymnasium, Motril, Spain

09/1995 - 12/2002

Physik-Studium, Granada Universität, Theoretische Physik (Abschluss: Master)

10/2006 - 06/2008

Mitarbeiter am CECAM (European Center of Atomic and Molecular Calculation), Ecole Normale Superieure de Lyon

07/2008 - 06/2010

Mitarbeiter am Institut Engineering Thermodynamics TU Delft (Abschluss: Dr. M.Sc.)

07-2010 - 08/2012

Postdoc am Institut für Technische Thermodynamik und Thermische Verfahrenstechnik (ITT), Stuttgart Universität

seit 09/2012

Wissenschaftlicher Mitarbeiter am Lehrstuhl für Thermodynamik (LTD), Technische Universität Kaiserslautern

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Letzte Änderung: 28.10.2014