Reversibly meltable layered alkylsiloxanes with melting points controllable by alkyl chain lengths

Fujii, Kazuko; Kodama, Hiroshi; Iyi, Nobuo; Fujita, Taketoshi; Kitamura, Kenji; Sato, Hisako; Yamagishi, Akihiko; Hayashi, Shigenobu

doi:10.1039/c3nj41008k

Cited by 5 publications

(35 citation statements)

References 32 publications

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“…became amorphous (as exemplified by the disappearance of the sharp diffraction peaks) for a threshold temperature as low as 46 ºC, similarly to reported results of hexadecyl silsesquioxane hybrids [46][47][48]. Such difference can be ascribed to the higher level of ordering of P1, with stronger cohesive forces inside the supramolecular materials hindering the thermal disordering of the product.…”

Section: P1 P3supporting

confidence: 85%

Non-symmetrical bis-silylated precursor can (also) self-direct the assembly of Silsesquioxane films

Chemtob

Croutxé‐Barghorn

et al. 2017

J Sol-Gel Sci Technol

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Symmetric α,ω-bis-silylated precursors are the standard building blocks of self-assembled bridged silsesquioxanes, a unique class of robust ordered nanomaterials prepared by sol-gel process without external surfactant. We report an unprecedented approach based on the utilization of a dissymmetric bis-silylated precursor, 1,2-bis(trimethoxysilyl)decane (1), in which the two alkoxy groups are carried by adjacent methylene groups. Extensive characterizationbased on X-ray diffraction, real-time FTIR, electron and optical microscopy, 29 Si solid-state NMR, thermogravimetry, and molecular modelingshows surprisingly that such non-symmetrical precursor is highly conducive to achieve highly ordered lamellar mesostructure, able to sustain temperature up to 120 °C. To emphasize the effect of the alkoxy group functionality and position, comparison is made systematically with analogous silsesquioxanes derived from bis-(2) and mono-silylated (3) precursors. The sol-gel polymerization of 1 is unique by its ability to produce a homogeneous film possessing structural characteristic on multiple scales: uniform microcrystallites consisting of nanolamellar organosilica hybrid material. The most likely mesostructure consists of bilayers of slightly interpenetrated trans C 8 H 9 chains, with a single central siloxy-hydrocarbon chain (Si 2 O(OH) 4-C 2 H 3) n. To permit a good lateral chain packing, the hydrocarbon chain of two adjacent silicon atoms point in opposite directions.

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Section: P1 P3supporting

confidence: 85%

Non-symmetrical bis-silylated precursor can (also) self-direct the assembly of Silsesquioxane films

Chemtob

Croutxé‐Barghorn

et al. 2017

J Sol-Gel Sci Technol

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“…This temperature corresponds to melting of the HDTMS hydrocarbon chains originating from the order−disorder arrangements of the hydrocarbon chains 57 and is the same as that reported by Fujii et al from heating to 150 °C. 58,59 As shown in Figure 5b, the cooling scan for bulk crystalline HDTMS showed an exothermic peak at around 37 °C corresponding to the crystallization of the HDTMS hydrocarbon chains. The temperature difference (5 K in this case) between melting and crystallization implies that the melting/crystallization transition for the HDTMS hydrocarbon chain is a supercooling process.…”

Section: ■ Results and Discussionmentioning

confidence: 94%

Development of Structure in Hexadecyltrimethoxysilane Adsorbed on Silica

2019

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The structural assemblies of hexadecyltrimethoxysilane (HDTMS) on silica particles were determined using temperature-modulated differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), and powder X-ray spectroscopy. At very small adsorbed amounts (<0.6 mg/m2), HDTMS molecules decomposed at a slightly higher temperature than bulk, exhibited symmetric and asymmetric FTIR resonances similar to those of liquid alkanes, showed a broad powder X-ray peak, and had a very small enthalpy of melting. These observations are consistent with poorly organized, disordered alkyl chains of directly attached molecules. At larger adsorbed amounts (>0.6 mg/m2 or more) in the “multilayer region”, the chains adopted more trans(anti) conformations, their decomposition temperatures approached those of the bulk condensed HDTMS, and a sharper primary powder X-ray peak was observed. Also, both melting and crystallization enthalpies for the bound HDTMS were found to exponentially approach the bulk enthalpy. In particular, the enthalpy changes were fitted with a linear dependence for the “sub-monolayer” and then an exponential approach to bulk with an exponential constant of about 1.6 mg/m2. Together, these changes provide insight into how adsorbed HDTMS molecules underwent structural changes, from directly bonded on the surface to bulklike material.

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“…No reversibly meltable layered inorganic-organic hybrid has been reported wherein the inorganic and organic moieties bond covalently to each other; 2 the only exceptions are the C n LSiloxanes reported previously by us and Bourlinos et al 6,7,14 In this report, the layered inorganic-organic hybrids with covalent bonds between the inorganic and organic moieties are referred to as ''layered covalently bonded inorganic-organic hybrids'' to distinguish them from the ''organoclays,'' which do not contain any covalent bonds. The inorganic and organic moieties are covalently bonded to each other and form a layered covalently bonded inorganic-organic hybrid monolith.…”

Section: Introductionmentioning

confidence: 95%

“…14 Finally, we synthesized reversibly meltable layered alkylsiloxanes (C n LSiloxanes) with melting points from À0.8 to 51.3 1C, controllable by the alkyl chain lengths. 7 Upon heating, the C n LSiloxanes liquefied at temperatures above the endothermic peaks observed by differential scanning calorimetry (DSC) (ESI †). The entire C n LSiloxanes including the siloxane sheet melt at the melting points (T m ) as observed in a water bath and under a microscope as reported previously, 7 in contrast to the ''organoclays'' and the other reported ''layered covalently bonded inorganic-organic hybrids''.…”

Section: Introductionmentioning

confidence: 99%

Structural changes of layered alkylsiloxanes during the reversible melting–solidification process

Fujii

Hayashi

Hashizume

et al. 2016

Phys. Chem. Chem. Phys.

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Through various in situ analyses, we have revealed the structural changes that occur during the reversible melting-solidification process of layered alkylsiloxanes (CnLSiloxanes) with carbon numbers (n) of 18 and 16. In situ high-resolution solid-state (13)C nuclear magnetic resonance (NMR) analysis at controlled temperatures indicates drastic conformational changes of the long alkyl chains during the melting-solidification process. A (13)C NMR signal at 33 ppm, which shows the highest intensity at room temperature (RT), is assigned to an inner methylene group with an all-trans conformation. As the temperature increases, the 33-ppm signal intensity decreases while the signal intensity at 30.5 ppm simultaneously increases. The 30.5 ppm signal is assigned to an inner methylene group with a trans-gauche conformation. Subsequently, upon cooling, the signal at 33 ppm recovers, even after CnLSiloxanes have melted. In situ X-ray diffraction measurements at controlled temperatures reveal that the ordered arrangement of the long alkyl chains becomes disordered with elevating temperatures and reordered upon cooling to RT. In situ high-resolution solid-state (29)Si NMR analysis shows that the melting-solidification process progresses without any structural change in siloxane sheets of the CnLSiloxanes. Thus, the in situ analyses show that disordering of the long alkyl chains causes the CnLSiloxanes to melt. Because the majority of long alkyl chains are packed again in the ordered arrangement with the all-trans conformation upon cooling, the CnLSiloxanes are reversibly solidified and the CnLSiloxane structure is recovered.

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Reversibly meltable layered alkylsiloxanes with melting points controllable by alkyl chain lengths

Cited by 5 publications

References 32 publications

Non-symmetrical bis-silylated precursor can (also) self-direct the assembly of Silsesquioxane films

Non-symmetrical bis-silylated precursor can (also) self-direct the assembly of Silsesquioxane films

Development of Structure in Hexadecyltrimethoxysilane Adsorbed on Silica

Structural changes of layered alkylsiloxanes during the reversible melting–solidification process

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