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Molecular dynamics simulations of

surfactant and nanoparticle self-

assembly at liquid-liquid interfaces

3 h 41 19/7

Abstract

We have performed molecular

dynamics (MD) simulations to

investigate self-assembly at water-

trichloroethylene (TCE) interfaces

with the emphasis on systems

containing modified (ci tin, iu

chnh) hydrocarbon nanoparticles

(1.2 nm in diameter) and sodium

dodecyl sulfate (sDs) surfactants.

The nanoparticles and surfactants

were first distributed randomly in the

water phase. The MD simulations

have clearly shown the progress of

migration and final equilibrium of

the sDs molecules at the water-TCE

interfaces with the nanoparticles

either at or in the vicinity of the

interfaces. One unique feature is the

attachment of surfactant molecules

to the nanoparticle clusters in the

water phase followed by the

detachment at the water-TCE

interfaces. At low concentrations of

surfactants, the surfactants and

nanoparticles co-equilibrate at the

interfaces. However, the surfactants,

at high concentrations, competitively

dominate the interfaces and deplete

nanoparticles away from the

interfaces. The interfacial properties,

such as interfacial thickness and

interfacial tension, are significantly

influenced by the presence of the

surfactants, but not the nanoparticles.

The order of the surfactants at the

interfaces increases with increasing

surfactant concentration, but is

independent of nanoparticle

M phng ng hc phn t qu

trnh t sp xp ca cc phn t hot

ng b mt v ht nano cc b

mt phn cch gia hai lp cht lng

Tm tt

Chng ti tin hnh cc m phng

ng hc phn t (MD) khm ph

hin tng t sp xp ti cc b mt

phn cch nc-trichloroethylene

(TCE), y chng ta s tp trung

vo cc h cha cc ht nano

hydrocarbon ci tin (ng knh 1.2

nm) v cc cht hot ng b mt

natri dodecyl sulfate (SDS). Trong

m phng, u tin, chng ta s cho

cc ht nano v cc cht hot ng

b mt phn tn ngu nhin trong

pha nc. Cc m phng MD gip

chng ta hiu r hn qu trnh di

chuyn v cn bng cui cng ca

cc phn t sDs ti cc b mt phn

cch nc-TCE khi c cc ht nano

nm ngay ti hoc ln cn cc b mt

phn cch. Mt tnh cht c o l

"hin tng gn" cc phn t hot

ng b mt vo cc m ht nano

trong pha nc, tip theo sau l 'tch

ra' cc b mt phn cch nc-

TCE. Khi nng cht hot ng b

mt thp, cc cht hot ng b mt

v ht nano cng cn bng cc b

mt phn cch. Tuy nhin, khi nng

ca cc cht hot ng b mt

cao, chng s chim u th cc b

mt phn cch v y cc ht nano ra

khi b mt phn cch. Cc cht hot

ng b mt c nh hng ng k

n cc thuc tnh b mt phn cch,

chng hn nh dy b mt phn

cch v sc cng mt phn cch,

nhng cc ht nano khng nh

hng n nhng tnh cht ny. Trt

t ca cc cht hot ng b mt

concentration. Finally, the simulation

has shown that surfactants can

aggregate along the water-TCE

interfaces, with and without the

presence of nanoparticles.

(some figures in this article are in

colour only in the electronic version)

Self-assembly of nanosized objects

at liquid-liquid interfaces is of

tremendous interest for various

natural and industrial applications.

For example, self-assembly of

surfactant molecules or polymers at

liquid-liquid interfaces is essential in

the preparation and stabilization of

conventional emulsions. The

importance of conventional

emulsions is reflected through their

wide applications in the food,

cosmetic, pharmaceutical, petroleum,

fine chemical, and coating industries.

Surfactant interfacial self-assembly

is also critical in numerous processes

such as lubrication, detergency,

biological transferring, and polymer

processing. Recently, there has been

a growing interest in the self-

assembly of nanoparticles due to

their important applications. For

example, self-assembled

nanoparticles at a liquid-liquid

interface serve as building blocks for

bottom-up assembly of new

functional materials with unique

physical properties [1, 2].

Furthermore, there is growing

interest in solid-stabilized emulsions

that use solid nanoparticles or

microparticles as emulsion

tng theo nng ca n, nhng

khng ph thuc nng ht nano.

Cui cng, m phng cho thy cc

cht hot ng b mt c th tch t

dc theo cc b mt phn cch nc-

TCE, khi c v khi khng c cc ht

nano.

(mt s nh trong bi bo ny l nh

mu v ch c th xem c trong

phin bn in t)

Hin tng t sp xp ca cc i

tng kch thc nano ti cc b mt

phn cch gia hai lp cht lng rt

ng quan tm trong t nhin cng

nh trong cc ng dng cng nghip.

V d, s t sp xp cc phn t hot

ng b mt v cc polyme b mt

phn cch gia hai lp cht lng

ng vai tr quan trng trong qu

trnh iu ch v n nh cc nh

tng thng thng. Tm quan trng

ca nh tng thng c th hin

qua cc ng dng a dng ca chng

trong thc phm, m phm, dc

phm, du kh, ha cht tinh khit,

v cc ngnh sn ph. T sp xp b

mt phn cch ca cht hot ng b

mt cng rt quan trng trong nhiu

qu trnh nh bi trn, ty ra,

chuyn i sinh hc, ch bin

polymer. Gn y, cc nh nghin

cu ngy cng quan tm n hin

tng t sp xp ca cc ht nano do

nhng ng dng quan trng ca

chng. V d, cc ht nano t sp xp

ti b mt phn cch gia hai lp

cht lng ng vai tr l nhng thnh

phn c bn trong qu trnh tng hp

t di ln cc vt liu chc nng

mi vi nhng tnh cht vt l c

o [1, 2]. Bn cnh , cc nh

nghin cu cng ngy cng quan tm

hn n cc nh tng n nh rn

stabilizers. For these systems, the

self-assembly of solid particles at

liquid-liquid interfaces is essential

[3-12]. Although the fundamentals of

surfactant adsorption at liquid-liquid

interfaces are well understood, the

self-assembly of nanoparticles at

liquid-liquid interfaces has not been

fully explored.

One of the remaining challenges is to

understand multiphase interactions,

self-assembly processes, and self-

assembled structures of

nanoparticles, especially when the

size of the nanoparticles is

comparable with the molecular

dimension of the surrounding liquids.

Dai et al [12] have reported the

success of using solid- stabilized

emulsions as a new experimental

model system to investigate the

detailed self-assembled structure of

nanoparticles (1-5 nm) at a water-

trichloroethylene (TCE) interface.

This assembly was determined by

use of an environmental transmission

electron microscope (E-TEM). In

sharp contrast to microparticles or

large-size nanoparticles forming a

monolayer at liquid-liquid interfaces,

ultra small dodecanethiol-capped

nanoparticles of 1-5 nm form

randomly distributed multilayers at

the water-TCE interfaces, with an

interparticle distance varying from

close contact to approximately 25 nm

[12]. This interesting result offers the

first direct observation of

nanoparticles in a liquid medium

using E-TEM and opens new

opportunities for high-resolution

dng cc ht nano v cc ht micro

rn lm cht n nh ha nh tng.

i vi cc h ny, hin tng t sp

xp cc ht rn ti b mt phn cch

gia hai lp cht lng rt quan trng

[3-12]. Mc d, chng ta hiu

c cc nguyn tc c bn ca hin

tng hp th cht hot ng b mt

ti cc b mt phn cch gia hai lp

cht lng, hin tng t sp xp ca

cc ht nano ti b mt phn cch

gia hai lp cht lng vn cha c

nghin cu thu o. Mt trong

nhng thch thc vn cn tn ti l

cc tng tc nhiu pha, cc qu

trnh t sp xp, v cc cu trc t

lp rp ca cc ht nano, c bit khi

kch thc ca cc ht nano vo c

kch thc ca phn t cht lng

xung quanh. Dai v cc cng s [12]

tuyn b thnh cng trong vic s

dng cc nh tng n nh rn lm

h m hnh th nghim mi kho

st chi tit cu trc t sp xp ca

cc ht nano (1-5 nm) ti b mt

phn cch nc-trichloroethylene

(TCE). Qu trnh lp ghp ny c

xc nh bng knh hin vi in t

truyn qua thn thin mi trng (E-

TEM). Khc vi cc ht micro hoc

ht nano kch thc ln hnh thnh

mt n lp b mt phn cch gia

hai lp cht lng, cc ht nano ph

dodecanethiol siu nh kch thc t

1-5 nm hnh thnh nhiu lp phn b

ngu nhin ti cc b mt phn cch

nc-TCE, trong khong cch

gia cc ht thay i t khng (chm

vo nhau) n khong 25 nm [12].

Kt qu l th ny gip chng