Melting of monolayer protected cluster superlattices

Sandhyarani, N.; Antony, M. P.; Selvam, G. Panneer; Pradeep, Thalappil

doi:10.1063/1.1322029

Cited by 53 publications

(80 citation statements)

References 46 publications

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“…DSC shows that, in systems below C 8 , melting is featureless; however, for longer chain lengths, a sharp feature is observed at a temperature close to the corresponding chain melting temperature. This is evidenced by both IR 46 and neutron scattering 50,51 measurements. However, neutron scattering data clearly show that there are significant interchain interactions in the smaller chain length thiols, making the dynamics evolve only slowly, and a higher temperature is needed to achieve total rotational freedom.…”

Section: Discussionmentioning

confidence: 88%

“…More details can be obtained from our earlier papers. 46,53,54 The experimental methodology for QENS has been presented in an earlier paper. 50 Briefly, the experiments were carried out using a medium-resolution quasielastic spectrometer at the Dhruva reactor in Trombay.…”

Section: Methodsmentioning

confidence: 99%

“…In the repeated cycles, an increase in enthalpy of this transition is observed, and is more pronounced in Ag clusters. Ex situ IR measurements 46 of the sample (after heating/cooling cycles) show the splitting of the methylene scissoring and rocking modes, which is an indication of more ordered structure. 47 This is attributed to the annealing of the monolayer on the surface.…”

Section: Introductionmentioning

confidence: 99%

“…46 The d + and d -(symmetric and asymmetric methyl stretching) modes show a blue shift at higher temperature. This suggests the melting of the alkyl chain.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Alkyl Chains in Monolayer-Protected Au and Ag Clusters and Silver Thiolates: A Comprehensive Quasielastic Neutron Scattering Investigation

et al. 2004

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Temperature-dependent dynamics of monolayer-protected Au and Ag nanoclusters and silver thiolates have been investigated with quasielastic neutron scattering. The simplest motion in these systems is the uniaxial rotation of the chain, which evolves slowly with temperature. While longer chain monolayers (above C 8 ) on Au clusters are rotationally frozen at room temperature, dynamic freedom exists in lower chain lengths. In the superlattice solids of Ag clusters, the dynamics evolve slowly, and at superlattice melting, all the chains are dynamic. The data are consistent with a structure in which the monolayers form bundles on the planes of metal clusters and such bundles interdigitate, forming the cluster assemblies. In thiolates, the dynamics is distinctly different in long-and short-chain systems. It arises abruptly at the melting temperature in C 12 but a bit sluggishly in C 18 , whereas in C 6 and C 8 , it evolves with temperature. The data are correlated with temperature-dependent infrared spectroscopy, which preserves some of the progression bands even after the bulk melting temperature, but loses them completely above 498 K, suggesting a possible partially ordered phase in this temperature window. Our studies have established the fact that (a) no rotational freedom exists in several of the alkyl chain monolayers on metal cluster solids at room temperature, (b) simple uniaxial rotation explains the dynamics of these systems, (c) the dynamics evolves slowly, and (d) such motions arise abruptly in long-chain layered thiolates which are similar to planar thiolates. We find that longer chains can possess conformational defects at higher temperatures, which slow the rotational dynamics.

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Section: Discussionmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…46 The d + and d -(symmetric and asymmetric methyl stretching) modes show a blue shift at higher temperature. This suggests the melting of the alkyl chain.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Alkyl Chains in Monolayer-Protected Au and Ag Clusters and Silver Thiolates: A Comprehensive Quasielastic Neutron Scattering Investigation

et al. 2004

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“…They have shown that alkanethiols undergo a melting transition at higher temperature, as in the case of Au SAMs. We have shown that layered octadecanethiolate melts at 400 K, much higher than the phase-transition temperature of planar monolayers [57]. This is attributed to the increase in van der Waals interaction as a result of the interdigitation of alkyl chains from the neighboring layer.…”

Section: Phase Transitionsmentioning

confidence: 91%

Structure and dynamics of monolayers on planar and cluster surfaces

Pradeep

Sandhyarani

2002

Pure and Applied Chemistry

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Organized molecular assemblies have been one of the intensely pursued areas of contemporary chemistry. Among the various methodologies used to make organized monolayer structures, self-assembled monolayers (SAMs) have been attractive to many materials chemists owing to the simplicity of the preparative method and high stability. Advances in various techniques and their application in the study of SAMs have significantly improved our understanding of these molecular systems. These studies have been further intensified since the successful preparation of stable metal clusters protected with monolayers. This article reviews the structure, temperature-induced phase transitions, and associated dynamics of monolayers, principally in the context of our own work in this area. Alkanethiols on Au (111) and Ag(111) are taken as archetypal systems to discuss the properties of 2D SAMs; studies from our laboratory have been on evaporated thin films. Alkanethiols on Au and Ag cluster surfaces are taken as examples of 3D SAMs. Although our principal focus will be on alkanethiols, we will touch upon a few other adsorbate systems as well.

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Synthesis of Nanofluids

Das

Choi

et al. 2007

Nanofluids

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In this chapter we are concerned with the synthesis of a diverse variety of nanofluids. As this book is concerned with nanofluids designed for specific applications, we limit our discussion to stable nanofluids and free-standing nanosystems which may be made in the form of fluids. Although the first category of fluids may not be separable into the constituent phases (i.e., solid and liquid), the other is in the separated phases to begin with. Nanoparticles formed in porous media such as zeolites, and embedded particles in glasses are not dealt with, although in a larger sense, particles in solids may be considered as solutions.From a general perspective, a two-phase colloidal system can be classified in terms of a dispersed phase and a dispersion medium. The dispersed phase and dispersion medium can be any one of the three phases (i.e., gas, liquid, or solid) except that the first category (i.e., gas in gas) is unknown. From this, a solid nanoparticle dispersed in an amorphous solid may be considered as a colloidal system and consequently, a nanofluid. In our descriptions, fluids will be liquids at ordinary conditions of temperature and pressure, and for that reason, supercritical fluids and gases as the dispersion phase are not considered. It may be noted that the synthesis of nanoparticles in these media (i.e., solid matrices 1 and supercritical fluids 2 ) is a large and advanced area of science. From a historical perspective, it is also important to remember that some of the early applications of nanoparticles were in the form of embedded particles in glasses. 3 Supercritical fluids are a recent area of development in nanoparticle science. GENERAL ISSUES OF CONCERNThere are several factors of interest when considering a given synthetic approach:(1) thermal stability, (2) dispersability in diverse media, and (3) chemical compatibility and ease of chemical manipulation. Each of these parameters is discussed in some detail below. It should be noted that several are intimately connected to each other.

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Melting of monolayer protected cluster superlattices

Cited by 53 publications

References 46 publications

Dynamics of Alkyl Chains in Monolayer-Protected Au and Ag Clusters and Silver Thiolates: A Comprehensive Quasielastic Neutron Scattering Investigation

Dynamics of Alkyl Chains in Monolayer-Protected Au and Ag Clusters and Silver Thiolates: A Comprehensive Quasielastic Neutron Scattering Investigation

Structure and dynamics of monolayers on planar and cluster surfaces

Synthesis of Nanofluids

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