139,144 research outputs found
Growth saturation of unstable thin films on transverse-striped hydrophilic-hydrophobic micropatterns
Using three-dimensional numerical simulations, we demonstrate the growth
saturation of an unstable thin liquid film on micropatterned
hydrophilic-hydrophobic substrates. We consider different transverse-striped
micropatterns, characterized by the total fraction of hydrophilic coverage and
the width of the hydrophilic stripes. We compare the growth of the film on the
micropatterns to the steady states observed on homogeneous substrates, which
correspond to a saturated sawtooth and growing finger configurations for
hydrophilic and hydrophobic substrates, respectively. The proposed
micropatterns trigger an alternating fingering-spreading dynamics of the film,
which leads to a complete suppression of the contact line growth above a
critical fraction of hydrophilic stripes. Furthermore, we find that increasing
the width of the hydrophilic stripes slows down the advancing front, giving
smaller critical fractions the wider the hydrophilic stripes are. Using
analytical approximations, we quantitatively predict the growth rate of the
contact line as a function of the covering fraction, and predict the threshold
fraction for saturation as a function of the stripe width.Comment: 11 pages, 5 figure
Random Hydrophilic-Hydrophobic Copolymers
We study a single statistical amphiphilic copolymer chain AB in a selective
solvent (e.g.water). Two situations are considered. In the annealed case,
hydrophilic (A) and hydrophobic (B) monomers are at local chemical equilibrium
and both the fraction of A monomers and their location along the chain can
vary, whereas in the quenched case (which is relevant to proteins), the
chemical sequence along the chain is fixed by synthesis. In both cases, the
physical behaviour depends on the average hydrophobicity of the polymer chain.
For a strongly hydrophobic chain (large fraction of B), we find an ordinary
continuous collapse, with a large conformational entropy in the
collapsed phase. For a weakly hydrophobic, or a hydrophilic chain, there is an
unusual first-order collapse transition. In particular, for the case of
Gaussian disorder, this discontinuous transition is driven by a change of sign
of the third virial coefficient. The entropy of this collapsed phase is
strongly reduced with respect to the collapsed phase. Email contact:
[email protected]: Saclay-T94/077 Email: [email protected]
Hydrophilic Matrices for Oral Control Drug Delivery
Oral controlled drug delivery has gathered tremendous attention over the years due to its many advantages over conventional dosage forms. Polymer-based matrices have become an integral part of the pharmaceutical industry. Hydrophilic matrices are capable of controlling the release of drug over an extended period of time. Hydrophilic polymers, especially the hydrophilic derivatives of cellulose ethers, are frequently used for these applications. Therefore, the objective of this review is to discuss the scientific and physicochemical aspects of these polymeric systems that can affect the drug release from such formulation
Water structuring and collagen adsorption at hydrophilic and hydrophobic silicon surfaces
The adsorption of a collagen fragment on both a hydrophobic,
hydrogen-terminated and a hydrophilic, natively oxidised Si surface is
investigated using all-atom molecular dynamics. While favourable direct
protein-surface interactions via localised contact points characterise adhesion
to the hydrophilic surface, evenly spread surface/molecule contacts and
stabilisation of the helical structure occurs upon adsorption on the
hydrophobic surface. In the latter case, we find that adhesion is accompanied
by a mutual fit between the hydrophilic/hydrophobic pattern within the protein
and the layered water structure at the solid/liquid interface, which may
provide an additional driving force to the classic hydrophobic effect
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Fabrication, characterisation and performance of hydrophilic and super-hydrophilic silica as cell culture surfaces
We demonstrate a straightforward procedure for the controlled formation of silica films on tissue culture polystyrene (PS) surfaces. The films were formed by sequentially treating PS with polyaniline, glutaric dialdehyde and protein prior to silica formation. The films could be tailored to exhibit superhydrophilicity (contact angle < 5°) which was retained for more than two months under ambient conditions. Both hydrophilic and super-hydrophilic silica coated surfaces were suitable for the culture of an adherent human melanoma cell line. Proliferation, toxicity and adhesion assays were used to compare cell behaviour. Cells on the silica surfaces showed enhanced adhesion and comparable rates of cell proliferation as compared to cells grown on conventional tissue culture plastic. The results obtained can be understood by considering the surface properties of the different materials and the ability of the silica coated surfaces to adsorb significantly higher levels of serum proteins from the growth medium. One of the outcomes of this study is a re-evaluation of the hydrophobicity/hydrophilicity characteristics required for good cell growth and the possibility of designing new tissue culture materials capable of greater control over cell populations
Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters
A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, ß-methyl-l-aspartate, and ß-benzyl-l-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr. \ud
The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction
How ions in solution can change the sign of the critical Casimir potential
We show that hydrophilic ions present in a confined, near-critical aqueous
mixture can lead to an attraction between like charge surfaces with opposing
preferential adsorption of the two species of the mixture, even though the
corresponding Casimir potential in uncharged systems is repulsive. This
prediction agrees with recent experiment [Nellen {\it{et al.}}, Soft
Matter{\bf{80}}, 061143 (2011)]. We also show that oppositely charged
hydrophobic surfaces can repel each other, although the Casimir potential
between uncharged surfaces with like preferential adsorption (selectivity) is
attractive. This behavior is expected when the electrostatic screening length
is larger than the correlation length, and one of the confining surfaces is
strongly selective and weakly charged, whereas the other confining surface is
weakly selective and strongly charged. The Casimir potential can change sign
because the hydrophilic ions near the weakly hydrophobic surface can
overcompensate the effect of hydrophobicity, and this surface can act as a
hydrophilic one. We also predict a more attractive interaction between
hydrophilic surfaces and a more repulsive interaction between hydrophobic
surfaces than given by the sum of the Casimir and Deby-H\"uckel potentials. Our
theory is derived systematically from a microscopic approach, and combines the
Landau-type and Debye-H\"uckel theories with an additional contribution of an
entropic origin
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