Structure and Dynamics of Nanoconfined Water Between Surfactant Monolayers

Abstract

The properties of nanoconfined water arise in direct response to the properties of the interfaces that confine it. A great deal of research has focused on understanding how and why the physical properties of confined water differ greatly from the bulk. In this work, we have used all-atom molecular dynamics (MD) simulations to provide a detailed description of the structural and dynamical properties of nanoconfined water between two monolayers consisting of an archetypal ionic surfactant, cetrimonium bromide (CTAB, [CH 3 (CH 2) 15 N(CH 3) 3 ] + Br −). Small differences in the area per surfactant of the monolayers impart a clear effect on the intrinsic density, mobility and ordering of the interfacial water layer confined by the monolayers. We find that as the area per surfactant within a monolayer decreases, the mobility of the interfacial 1 water molecules decreases in response. As the monolayer packing density decreases, we find that each individual CTAB molecule has a greater effect on the ordering of water molecules in its first hydration shell. In a denser monolayer, we observe that the effect of individual CTAB molecules on the ordering of water molecules is hindered by increased competition between headgroups. Therefore, when two monolayers with different areas per surfactant are used to confine a nanoscale water layer, we observe the emergence of non-centrosymmetry.

Surface hydration for antifouling and bio-adhesion

“…15 At an even smaller scale, nanoconned water between the surface and adsorbate can be structured, no longer behaving in the way that we usually think of bulk solvent and possibly illustrating how surface hydration can be benecial. 68 With data shown here, we may now be seeing the rst known instance of interfacial hydration contributing to the underwater bonding of a curing bioadhesive.…”

Understanding the pH-Directed Self-Assembly of a Four-Arm Block Copolymer

“…It is challenging to quantify the structure of these clusters. Intrinsic interface approaches have been widely applied to study the complex interfacial structure of self-assembled micelles , and monolayers. , For this work, we have developed an intrinsic core–shell interface (ICSI) identification methodology by adapting the approach that we previously developed for analyzing rough and patchy surfactant monolayers . Some approaches rely on well-defined anchor atoms to make up the intrinsic surface, while probe-based methods are used in other techniques. , Here, because we do not have well-defined anchor atoms, we construct a surface that maps the core–shell interface of the cluster (including free unimers in solution) by automatically choosing the non-hydrogen PO atoms atoms to build the ICSI for each cluster (PO atoms typically make up a loose hydrophobic core; see Figure ).…”

“…The intrinsic VHSCF profile, G̃ s ( r ,τ), of water surrounding the clusters is calculated as where r i ( t ) is the position of a given water oxygen atom at time t and the lag time τ = 20 ps. The intrinsic VHSCF profile provides detailed spatial resolution in r that cannot be obtained with time-averaged diffusion coefficients …”

“…The intrinsic VHSCF profile provides detailed spatial resolution in r that cannot be obtained with time-averaged diffusion coefficients. 60 Other Analysis Methods. To determine the size of the T304 clusters in our simulations, we calculate the radius of gyration and the hydrodynamic radius of each cluster.…”

Redefining the concept of hydration water near soft interfaces

“…23 However, the interface forms instantaneous layers that can be revealed using several advanced definitions. [26][27][28][29][30][31][32] Here, we follow Pandit et al, 26 because it allows us to introduce the instantaneous local distance ξ. The metric ξ is defined as the distance of each water molecule from the closest cell of a Voronoi tessellation centered on the phosphorous and nitrogen atoms of the phospholipid heads (Fig.…”