Dispersion stability and rheological properties of silica suspensions in aqueous solutions

The Effects of Friction and Temperature in the Chemical-Mechanical Planarization Process

Chemical-mechanical planarization (CMP) represents the preferred technology in which both chemical and mechanical interactions are combined to achieve global planarization/polishing of wafer surfaces (wafer patterns from metal with a selective layer, in this paper). CMP is a complex process of material removal process by friction, which interferes with numerous mechanical and chemical parameters. Compared with chemical parameters, mechanical parameters have a greater influence on the material removal rate (MRR). The mechanical parameters manifest by friction force (F_f) and heat generated by friction in the CMP process. The F_f can be estimated by its monitoring in the CMP process, and process temperature is obtained with help of an infrared rays (IR) sensor. Both the F_f and the MRR increase by introducing colloidal silica (SiO₂) as an abrasive into the selective layer CMP slurry. The calculated wafer non-uniformity (WNU) was correlated with the friction coefficient (COF). The control of F_f and of the slurry stability is important to maintain a good quality of planarization with optimal results, because F_f participates in mechanical abrasion, and large F_f may generate defects on the wafer surface. Additionally, the temperature generated by the F_f increases as the SiO₂ concentration increases. The MRR of the selective layer into the CMP slurry showed a non-linear (Prestonian) behavior, useful not only to improve the planarization level but to improve its non-uniformity due to the various pressure distributions. The evaluation of the F_f allowed the calculation of the friction energy (E_f) to highlight the chemical contribution in selective-layer CMP, from which it derived an empirical model for the material removal amount (MRA) and validated by the CMP results. With the addition of abrasive nanoparticles into the CMP slurry, their concentration increased and the MRA of the selective layer improved; F_f and MRR can be increased due to the number of chemisorbed active abrasive nanoparticles by the selective layer. Therefore, a single abrasive was considered to better understand the effect of SiO₂ concentration as an abrasive and of the MRR features depending on abrasive nanoparticle concentration. This paper highlights the correlation between friction and temperature of the SiO₂ slurry with CMP results, useful to examine the temperature distribution. All the MRRs depending on E_f after planarization with various SiO₂ concentrations had a non-linear characteristic. The obtained results can help in developing a CMP process more effectively.

Role of Fine Silica as Amorphous Solid Dispersion Carriers for Enhancing Drug Load and Preventing Recrystallization- A Comprehensive Review

Amorphous solid dispersion (ASD) is a popular concept for improving the dissolution and oral bioavailability of poorly water-soluble drugs. ASD faces two primary challenges of low drug loading and recrystallization upon storage. Several polymeric carriers are used to fabricate a stable ASD formulation with a high drug load. The role of silica in this context has been proven significant. Different types of silica, porous and nonporous, have been used to develop ASD. Amorphous drugs get entrapped into silica pores or adsorbed on their surface. Due to high porosity and wide surface area, silica provides better drug dissolution and high drug loading. Recrystallization of amorphous drugs is inhibited by limited molecular ability inside the delicate pores due to hydrogen bonding with the surface silanol groups. A handful of researches have been published on silica-based ASD, where versatile types of silica have been used. However, the effect of different kinds of silica on product stability and drug loading has been rarely addressed. The present study analyzes multiple porous and nonporous silica types and their distinct role in developing a stable ASD. Emphasis has been given to various types of silica which are commonly used in the pharmaceutical industry.

Assessment of Physical, Mechanical, Biopharmaceutical Properties of Emulgels and Bigel Containing Ciclopirox Olamine

Emulsions are thermodynamically unstable systems and it is difficult to produce biphasic formulations with large amounts of oil. The aim of our study was to prepare biphasic formulations containing 1% ciclopirox olamine and to determine the influence of the method of oil incorporation (without and with emulsifier and gelifier) on the physical (pH, particle size, rheological properties), mechanical, and biopharmaceutical properties of the formulations. It was found that the use of a poloxamer 407 gel as the hydrophase could result in a stable formulation when an oil with (EPG) or without an emulsifier (APG) or oleogel (OPG) was used as the oily phase. The results of the studies showed that the addition of an emulsifier (polysorbate 80) led to a decrease in the sol-gel temperature, a slower release of ciclopirox olamine, and a higher stability in the freeze–thaw test. However, regardless of the way the oil is incorporated, the particles are distributed in the same range and the antifungal activity against T. rubrum is the same. It is possible to create a biphasic formulation with a large amount of oil and poloxamer gel, but for greater stability, it is recommended to include an emulsifier in the composition.

A multiscale time-Laplace method to extract relaxation times from non-stationary dynamic light scattering signals

Dynamic Light Scattering (DLS) is a well-known technique to study the relaxation times of systems at equilibrium. In many soft matter systems, we actually have to consider non-equilibrium or non-stationary situations. We discuss here the principles, the signal processing techniques we developed, based on regularized inverse Laplace transform, sliding with time, and the light scattering signal acquisition, which enable us to use DLS experiments in this general situation. In this article, we show how to obtain such a time-Laplace analysis. We claim that this method can be adapted to numerous DLS experiments dealing with non-equilibrium systems so as to extract the non-stationary distribution of relaxation times. To prove that, we test this time-Laplace method on three different non-equilibrium processes or systems investigated by means of the DLS technique: the cooling kinetics of a colloidal particle solution, the sol-gel transition and the internal dynamics of a living cell nucleus.

Rheological Properties of MWCNT-Doped Titanium-Oxo-Alkoxide Gel Materials for Fiber Drawing

A strategy of doping by multi-walled carbon nanotubes (MWCNT) to enhance mechanical strength and the electrical conductivity of ceramic fibers has nowadays attracted a great deal of attention for a wide variety of industrial applications. This study focuses on the effect of MWCNTs on rheological properties of metal alkoxide precursors used for the preparation of nanoceramic metal oxide fibers. The rheological behavior of MWCNT-loaded titanium alkoxide sol precursors has been evaluated via an extensional rheometry method. A substantial decrease in elongational viscosity and relaxation time has been observed upon an introduction of MWCNTs even of low concentrations (less than 0.1 wt.%). A high quality MWCNT/nanoceramic TiO₂ composite fibers drawn from the specified precursors has been validated. The MWCNT percolation, which is mandatory for electrical conductivity (50 S/m), has been achieved at 1 wt.% MWCNT doping.

MXene (Ti3C2Tx) as a Promising Substrate for Methane Storage via Enhanced Gas Hydrate Formation

Methane hydrate (MH) makes it possible to store methane using the cheapest and safest solvent: water. However, the sluggish formation kinetics hinders its practical utilization. Recently, the use of nanomaterials has been suggested as a potential solution; however, there is still a lack of high-efficiency kinetic promotors, and the promoting mechanism remains unclear. Herein, we demonstrated that MXene dispersion is promising for the storage of methane via MH with rapid formation kinetics, high storage capacity, and impressive cyclic stability. MXene can significantly shorten the induction time for MH formation. The enhanced kinetics was achieved by providing extra nucleation sites and enhancing thermal conductivity, although the increased surface tension of MXene dispersion could impede the MH formation via limited mass transfer. We confirmed that the concentration-dependent promoting effect of MXene dispersions results from regulating the assembly of water molecules. The insight of this work can apply to develop high-efficiency additives to control the formation kinetics of MH.

Hydrophobic Modification on the Surface of SiO2 Nanoparticle: Wettability Control

Good control of the morphology, particle size, and wettability of silica nanoparticles is of increasing importance to their use in a variety of fields. Here, we propose a strategy to tune the surface wettability of nanosilica by changing the dosage of a chemical modifier. A series of measurements, including scanning electron microscopy (SEM), laser scatting technique, Fourier transform infrared (FTIR) spectroscopy, thermogravimetry, and surface hydroxyl number and water contact angle measurement, were conducted to verify the surface chemistry and wettability of these nanoparticles. Through controlled chemical modification, the contact angle of the treated nanoparticles increases from 34.7 to 155° with increasing amount of dichlorodimethylsilane (DCDMS) within a molar ratio (MR) between DCDMS and nanoparticles of 5.17. The number of hydroxyl groups covered on the particle surface decreases gradually from 1.79 to 0.47, and the surface grafting rate could reach 73.7%. As the addition of dichlorodimethylsilane equals MR 5.17, the contact angle reaches the maximum value of 155°, which displays excellent superhydrophobicity. After surpassing the point of MR 5.17, the contact angle does not increase but starts to decrease, ultimately remaining stable at 135°. It can be concluded that the surface wettability of nano-SiO₂ particles can be precisely modulated by varying the amounts of the modifier. Furthermore, the modulating mechanism of the process occurring on the surface of SiO₂ particles has been investigated at the molecular level.