Quartz Crystal Microbalance Substrate Research Articles

An Unconventional Immunosensor for Biomolecule Detection via Nonspecific Gold Nanoparticle-Antibody Interactions.

Immunogold, that is, gold nanoparticles (AuNPs) conjugated with biomolecules such as antibodies and peptides, have been widely used to construct sandwiched immunosensors for biodetection. Two main challenges in these immunoassays are difficulties in finding and validating a suitable antibody, and the nonspecific interaction between the substrate and immunogold, which lowers the detection sensitivity and even causes false results. To avoid these issues, we took advantage of the nonspecific interaction between AuNPs and capture antibodies and proposed a new sensing mechanism. That is, after the capture of analyte targets by the capture antibodies on the substrate, AuNPs of certain chemical functionality would preferably bind to the free capture antibodies. Consequently, the amount of deposited AuNPs will inversely depend on the concentration of the analytes. As a proof-of-concept, we designed a mass-based sensor where anti-IgG antibodies were coated on a quartz crystal microbalance substrate. After IgG was introduced, tannic acid-capped AuNPs were applied to bind with the free anti-IgG antibody molecules. A frequency change (Δf) of the quartz substrate was induced by the increased mass loading. To further amplify the loading mass, an Ag enhancer solution was added, and Ag growth was catalyzed by the bound AuNPs. The Δf response showed a concentration-dependent decrease when increasing IgG concentration with a detection limit of 2.6 ng/mL. This method relies on the nonspecific interaction between AuNPs and anti-IgG antibodies to realize sensitive detection of IgG and eliminates the use of detection antibodies. The concept is an alternative to many existing immunoassay technologies.

Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

Abstract The molecular size of alkaline cation has been reported to affect the dissolution of resist film in alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions was investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near surface was swollen by decreasing the size of alkaline cation. By either increasing or decreasing the size of alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.

Real-time kinetic analysis and detection of glycated hemoglobin A1c using a quartz crystal microbalance-based aptasensor.

Glycated hemoglobin (HbA1c) has been an important biomarker for long-term diagnosis and monitoring of diabetes mellitus. The development of a rapid, reliable, and less sophisticated device to measure HbA1c is imperative to facilitate efficient early-care diabetes management. To date, no existing aptamer-based biosensor (aptasensor) for detecting HbA1c has been developed using a quartz crystal microbalance (QCM). In this study, the aptamer specific to HbA1c as a novel biosensing receptor was covalently functionalized onto a QCM substrate via mixed self-assembled monolayers (SAMs). A portable QCM equipped with a liquid-flow module was used to investigate the biospecificity, sensitivity, and interaction dynamics of the aptamer functionalized surfaces. The real-time kinetic analysis of HbA1c binding to the surface-functionalized aptamers revealed "on" and "off" binding rates of 4.19 × 104 M-1 s-1 and 2.43 × 10-3 s-1, respectively. These kinetic parameters imply that the QCM-based aptasensor specifically recognizes HbA1c with an equilibrium dissociation constant as low as 57.99 nM. The linear detection of HbA1c spanned from 13 to 108 nM, with a limit of detection (LOD) of 26.29 nM. Moreover, the spiked plasma sample analysis offered compelling evidence that this aptasensor is a promising technique for developing a point-of-care device for diabetes mellitus.

An ultrasensitive micropillar-enabled acoustic wave (μPAW) microdevice for real-time viscosity measurement

Viscosity measurement has recently captured considerable attention due to its wide range of applications in fields such as pharmacy, food industry, cosmetic industry, and biomedical diagnostics. Acoustic wave sensors such as quartz crystal microbalance (QCM) are well-known mass sensors that also show their capability in measuring liquid viscosity. However, the challenges for QCM-based viscosity measurement devices lie in their low sensitivity and unstable response. Herein, we report an ultrasensitive micropillar-enabled acoustic wave (μPAW) viscometer by fabricating well-defined polymethyl methacrylate (PMMA) micropillars on a QCM substrate to achieve ultrahigh sensitivity for liquid viscosity with a stable response thanks to a unique vibration coupling between the micropillar and QCM substrate. The μPAW based viscometer shows a 20-fold improvement in the measurement sensitivity over traditional QCM viscometers and achieved an excellent limit of detection (LOD) while measuring the viscosity of sucrose liquid as low as 0.054 wt%. The microdevice developed in this work is a promising tool for the viscosity measurement of liquids.

Interfacial self‐assembly growth of mesoporous polydopamine nanofilms for formaldehyde sensing

AbstractMesoporous polymer nanofilms combine the advantages of the unique structure of mesopores, the quasi‐2D configuration of the films, and the inherent properties of polymers, and have become a kind of ideal candidate for the high‐performance micro‐nano devices due to their highly accessible surface area and exposed active sites. However, the facile preparation of polymer nanofilms with well‐defined mesostructures has remained a great challenge due to the lack of synthetic strategies. In this study, we developed a simple soft‐template interfacial co‐assembly strategy to in‐situ construct mesoporous polydopamine nanofilms with uniform thickness (30 nm) and regularly distributed mesopore arrays (average pore size of 12 nm) on surfaces with different types and morphologies. Furthermore, a single‐layer mesoporous polymer nanofilm was directly grown on a quartz crystal microbalance substrate and its performance for sensing formaldehyde was studied. The resulted sensor showed excellent sensing response, fast response/recovery dynamics, and great stability, presenting a great promising landscape for trace detection of formaldehyde gas.

High-Sensitivity and Environmentally Friendly Humidity Sensors Deposited with Recyclable Green Microspheres for Wireless Monitoring.

The reliable, high-sensitive, wireless, and affordable requirements for humidity sensors are needed in high-precision measurement fields. Quartz crystal microbalance (QCM) based on the piezoelectric effect can accurately detect the mass changes at the nanogram level. However, water-capture materials deposited on the surface of QCM generally show disadvantages in either cost, sensitivity, or recyclability. Herein, novel QCM-based humidity sensors (NQHSs) are developed by uniformly depositing green microspheres (GMs) of natural polymers prepared by the chemical synthesis of the emulsification/inner gel method on QCM as humidity-sensitive materials. The NQHSs demonstrate high accuracy and sensitivity (27.1 Hz/% RH) owing to the various hydrophilic groups and porous nano-3D deposition structure. Compared with the devices deposited with a smooth film, the frequency of the NQHSs shows almost no changes during the cyclic test and exhibits long-term stability. The NQHSs have been successfully applied to non-contact sensing human activities and remote real-time humidity monitoring via Bluetooth transmission. In addition, the deposited humidity-sensitive GMs and QCM substrate are fully recycled and reused (72% of the original value). This work has provided an innovative idea to construct environmental-friendly, high-sensitivity, and wireless humidity sensors.

Novel analysis of a micropillar coupled acoustic wave sensor

Acoustic wave sensors are being developed for many emerging applications such as in semiconductor fabrication, biological diagnostics and polymer characterization. Traditional acoustic wave sensing devices such as quartz crystal microbalance (QCM) rely on polymer thin films coated on quartz plates to detect chemical and biological agents. It has been found that significant sensitivity enhancement of QCM devices can be achieved by simply attaching a polymer micropillar film onto the QCM substrate (QCM-P) to enable a unique coupled resonance between the micropillars and quartz substrate. In the present work, an equivalent circuit model integrating mechanical vibration of micropillars and electrical load impedance of piezoelectric substrate was developed to predict the frequency shift and Q-factor of the QCM-P devices when operating in air and liquid environments. In the model, the vibration of micropillars was solved simultaneously with the liquid loading on the pillar surface. The resultant hydraulic force was integrated into the circuit model to predict the load impedance on the sensor surface. The developed model was validated by experimental results for QCM-P devices operating in air and water with different micropillar heights. It will serve as a powerful tool to predict the performance of the QCM-P devices for different applications.

High-Performance QCM Humidity Sensors Using Carbon Nanostructure Material as Sensing Film

Introduction Nowadays, sensors have become increasingly indispensable. It is particularly worth mentioning that the humidity has gradually become the standard for measuring environmental state and physical health. From the perspective of manufcturing, the performance and technical index of humidity sensors can vary greatly on materials, structures and processes. For instance, multiple sensing technologies including acoustic [1], resistance [2], optical [3], impedance [4],capacitance [5], thermal [6], and resonance [7], etc. have been explored to monitor the humidity. quartz crystal microbalance (QCM) has been proven to be an excellent mass sensing platform for humidity detection according to Sauerbrey’s equation [8].Sensitive material is the key of a QCM sensor. Among various materials, a variety of sensitive materials has been deposited on the electrode surface of QCM for detecting moisture, such as polymer, metal oxides, carbonic materials and so on. In this study, a series of high performance QCM humidity sensors were developed which using multi-walled CNTs (MWCNTs), Graphene quantum dots(GQDs), Chitosan(CS) and their composites as sensing film. The humidity sensing characteristics, such as dynamical response, reproducibility, and hysteresis characteristics were measured and discussed. Furthermore, the adsorption dynamics of water vapor molecules mechanism was also analyzed. Method Characterization Raman spectra were obtained on J-YT64000 Raman spectrometer with 633 nm wavelength incident laser light. The X-ray photoelectron spectroscopy (XPS) analysis was measured on an ESCALAB MK II Xray photoelectron spectrometer using Mg as exciting source. The Fourier transform infrared spectroscopy (FT-IR) spectra of as-prepared were obtained on a WQF-510AFTIR spectrometer, using KBr pellets as the reference. The transmission electron microscopy (TEM) images were taken by a JEM-2100F electron microscope (JEOL, Japan). Fabrication of QCM humidity sensor The QCM substrates used in this work were purchased from Beijing Chenjing Electronic Co., Ltd. China. The QCM was consisted of AT-cut quartz crystal (8 mm diameter) with a fundamental frequency of 10 MHz and silver electrodes (5 mm diameter) were covered on both sides, the electrode leaded two pins for testing purposes. As a typical procedure, the QCM substrates were ultrasonic cleaned by acetone, ethanol and deionized water for 10 min successively, and then dried in an air-tight container which filled with inert nitrogen gas for the whole night at room temperature. The QCM humidity sensor was obtained via dropping the as-prepared composites dispersion by micropipette on the Ag-electrodes surface of the QCM. Then, the modified QCM sensor was put into the foregoing container for at least 12 h. Results and Conclusions The humidity sensing characteristics of prepared QCM sensors were quantified by transforming the RH level ambient and measuring the shift of the vibration frequency. The humidity hysteresis performance, reproducibility and reversibility were also examined respectively. After further study, a plausible mechanism analysis for the above excellent sensitivity was given. In conclusion, an excellent QCM humidity sensor was obtained to detect full RH range. The oscillating circuit and impedance analysis methods have been adopted to examine the dynamic response and recovery behaviors and static humidity sensing performances, respectively. In addition, the intrinsic hydrophilicity is able to provide more water adsorption sites. The optimized QCM sensor demonstrated the highest humidity sensitivity and long-term stability, and tiny humidity hysteresis. The prepared QCM sensor is reliable for monitoring water vapor content in wide humidity range.

The Effect of Solution Concentration and Deposition Time on Viscoelasticity and Morphology of Polyaniline Coating

As one of the most studied conductive polymers, polyaniline (PANi) has a variety of applications, one of which is an active gas sensor, due to the presence of amine and imine groups in PANi that can easily react with gas. Quartz crystal microbalance (QCM) is a piezoelectric sensor with the working principle of frequency changes as a result of changes in mass on its surface. As an active gas sensor material on the QCM substrate, PANi must be deposited in the form of a thin layer. A good quality of thin film is if the film does not give loading the effect on QCM and has a homogeneous morphology. This research has succeeded in depositing PANi thin films by surface polymerization method by varying the parameters of PANi solution concentration and deposition time. Deposition parameters that are varied can be seen its effect on the viscoelasticity and morphology of PANi thin film formed. The viscoelasticity of the thin film was interpreted from the measurement of the thin layer impedance using an impedance analyser, while the morphology of the thin film was characterized using SEM. From the results of this study it was found that with the surface polymerization method, the PANi thin layer impedance value changes with the deposition time which is getting longer, but the change in impedance value is not significant and does not give a loading effect on QCM. At the same deposition time with different solution concentrations, the impedance value of the formed layer also does not give a loading effect on QCM. Although it has successfully deposited PANi with a surface polymerization method, the morphology of the PANi film formed is not yet homogeneous, as seen from the formation of PANi agglomeration on the QCM surface.

An ultrasensitive acoustic wave resonator device enabled by gluing a replaceable micropillar film

Traditional acoustic wave based sensing devices such as quartz crystal microbalance (QCM) rely on the thin films coated on the piezoelectric substrates as the sensing films for chemical and biological detection. This study demonstrates that significant sensitivity enhancement over traditional film based QCM (QCM-F) devices can be achieved by simply attaching a poly(methylmethacrylate) (PMMA) micropillar film onto a QCM substrate (QCM-P) by using a UV-curable glue. Humidity absorption measurements shows that the unique resonance occurred between the micropillars and the piezoelectric substrate improved the mass sensitivity of the QCM sensor by more than eight-fold. In addition, the newly developed QCM-P sensor and traditional QCM-F were utilized to detect bovine serum albumin (BSA) protein immobilization on PMMA surfaces. It was found that the glued QCM-P was capable of measuring BSA at a much lower concentration (200 nM) in comparison to QCM-F (1500 nM). The glue-based micropillar QCM device showed great potential for improving the sensitivity, simplifying the fabrication process, and reducing the cost of QCM sensors for various biosensing and chemical usages.

Chitosan-Based Quartz Crystal Microbalance for Alcohol Sensing

Short-chain alcohols are a group of volatile organic compounds (VOCs) that are often found in workplaces and laboratories, as well as medical, pharmaceutical, and food industries. Real-time monitoring of alcohol vapors is essential because exposure to alcohol vapors with concentrations of 0.15–0.30 mg·L−1 may be harmful to human health. This study aims to improve the detection capabilities of quartz crystal microbalance (QCM)-based sensors for the analysis of alcohol vapors. The active layer of chitosan was immobilized onto the QCM substrate through a self-assembled monolayer of L-cysteine using glutaraldehyde as a cross-linking agent. Before alcohol analysis, the QCM sensing chip was exposed to humidity because water vapor significantly interferes with QCM gas sensing. The prepared QCM sensor chip was tested for the detection of four different alcohols: n-propanol, ethanol, isoamyl alcohol, and n-amyl alcohol. For comparison, a non-alcohol of acetone was also tested. The prepared QCM sensing chip is selective to alcohols because of hydrogen bond formation between the hydroxyl groups of chitosan and the analyte. The highest response was achieved when the QCM sensing chip was exposed to n-amyl alcohol vapor, with a sensitivity of about 4.4 Hz·mg−1·L. Generally, the sensitivity of the QCM sensing chip is dependent on the molecular weight of alcohol. Moreover, the developed QCM sensing chips are stable after 10 days of repeated measurements, with a rapid response time of only 26 s. The QCM sensing chip provides an alternative method to established analytical methods such as gas chromatography for the detection of short-chain alcohol vapors.

Swelling Behavior in Solvent Vapor Sensing based on Quartz Crystal Microbalance (QCM) Coated Polyacrylonitrile (PAN) Nanofiber

Polyacrylonitrile (PAN) nanofiber deposited on quartz crystal microbalance (QCM) substrate as solvent vapor sensing has been successfully developed. The absorption and swelling behavior has been assumed to be responsible for sensing mechanism in vapor sensing. In this study, we aim to investigate the correlation between the swelling degree (polymer-solvent affinity) and the sensor response. The PAN nanofiber has been successfully deposited on QCM substrate with relatively homogenous nanofiber diameter about (260 ± 20) nm. The tests vapor solvent was included dimethylformamide (DMF), dimethylacetamide (DMAc), ethylene glycol (EG), toluene, ethanol, and distilled water. The results indicated that the sensor response for various vapor solvent clearly influences by its polymer-solvent affinity. The highest sensor response was achieved with DMF vapor due to its highest affinity with PAN polymer. The swelling behavior of polymer can be a potential candidate for developing vapor sensors with a polymer as an active layer.

Polyacrylonitrile nanofiber as polar solvent N,N-dimethyl formamide sensor based on quartz crystal microbalance technique

Here, we describe an N,N-dimethyl formamide (DMF) vapour sensor fabricated by coating polyacrylonitrile (PAN) nanofiber structured on quartz crystal microbalance (QCM). The PAN nanofiber sensors with an average diameter of 225 nm to 310 nm were fabricated via electrospinning process with different mass deposition on QCM substrate. The nanostructured of PAN nanofiber offers a high specific surface area that improved the sensing performance of nanofiber sensors. Benefiting from that fine structure, and high polymer-solvent affinity between PAN and DMF, the development of DMF sensors presented good response at ambient temperature. Since there is no chemical reaction between PAN nanofiber and DMF vapour, weak physical interaction such absorption and swelling were responsible for the sensing behavior. The results are indicating that the response of PAN nanofiber sensors has more dependency on the nanofiber structure (specific surface area) rather than its mass deposition. The sensor also showed good stability after a few days sensing. These findings have significant implications for developing DMF vapour sensor based on QCM coated polymer nanofibers.

Quartz Crystal Microbalance Coated with Vanadium Oxide Thin Film for $$\hbox {CO}_{2}$$ CO 2 Gas Sensor at Room Temperature

A gas-sensing device based on quartz crystal microbalance (QCM) covered with vanadium oxide thin film has been elaborated to detect $$\hbox {CO}_{2}$$ gas at room temperature. Vanadium oxide thin films were deposited onto QCM substrates by vacuum thermal evaporation technique. The vanadium oxide-coated QCM was heated at $$200\,^{\circ }\hbox {C}$$ for different times. The influence of the annealing time on structural and morphological properties of the deposited films was investigated by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The elaborated QCM/vanadium oxide structures were tested for $$\hbox {CO}_{2}$$ gas sensing. The results show that the sensor sensitivity increases with the annealing time due to the increase in the roughness of the surface. Moreover, the structure heated at $$200\,^{\circ }\hbox {C}$$ for 3 h exhibited a high resonance frequency shift ( $$\Delta f$$ ) under a $$\hbox {CO}_{2}$$ pressure of 40 mbar, fast response time (57 s), short recovery time (43 s), good stability, linearity, reproducibility, and reversibility.

The temperature effect of AT-cut input quartz parameters on QCM effective properties calculated with equivalent circuit models

In what follows, AT-cut quartz crystal microbalance (QCM) effective properties for two commercial QCM substrates, are calculated as a function of temperature, while varying the degree of implementation regarding the temperature dependence of input quartz parameters in the transmission line (TL) model. Results for the effective quartz viscosity, oscillation area and external capacitance, are in qualitative agreement per property, irrespective of the implemented, input quartz parameter set for the calculations. However, the effective quartz thickness accounts for the quartz thermal expansion effect, only when quartz density is temperature adjusted, whereas quantitative deviations in the effective oscillation area, are qualitatively explained in the light of literature correlations, which relate the implemented input quartz parameter set, with inherent QCM energy dissipation metrics, and the magnitude of energy trapping. Moreover, the varying degree of input quartz parameter adjustment with temperature, yields qualitative and quantitative deviations from the expected response, in terms of a QCM quality metric, the C0/C1 ratio. Results suggest that the precision in the determination of the static capacitance C0 and the QCM effective properties incorporated therein, can be improved, with potential improvements in relevant, liquid or gas phase QCM applications.

A Study of Drop-Microstructured Surface Interactions during Dropwise Condensation with Quartz Crystal Microbalance.

Dropwise condensation (DWC) on hydrophobic surfaces is attracting attention for its great potential in many industrial applications, such as steam power plants, water desalination, and de-icing of aerodynamic surfaces, to list a few. The direct dynamic characterization of liquid/solid interaction can significantly accelerate the progress toward a full understanding of the thermal and mass transport mechanisms during DWC processes. This work reports a novel Quartz Crystal Microbalance (QCM) based method that can quantitatively analyze the interaction between water droplets and micropillar surfaces during different condensation states such as filmwise, Wenzel, and partial Cassie states. A combined nanoimprinting lithography and chemical surface treatment approach was utilized to fabricate the micropillar based superhydrophobic and superhydrophilic surfaces on the QCM substrates. The normalized frequency shift of the QCM device together with the microscopic observation of the corresponding drop motion revealed the droplets growth and their coalescence processes and clearly demonstrated the differences between the three aforementioned condensation states. In addition, the transition between Cassie and Wenzel states was successfully captured by this method. The newly developed QCM system provides a valuable tool for the dynamic characterization of different condensation processes.

Quartz crystal microbalance gas sensor with nanocrystalline diamond sensitive layer

Gas sensors based on a quartz crystal microbalance (QCM) coated with nanocrystalline diamond (NCD) were developed and tested on NH3, CO2, and humidity detection at room temperature and compared with the bare (uncoated) QCM. NCD films were directly grown on the QCM by a large-area pulsed linear-antenna microwave plasma CVD process from the CH4/CO2/H2 gas mixture at temperatures below 400 °C. The as-grown NCD films on QCM and reference Si substrates were characterized by scanning electron and atomic force microscopies as well as Raman and optical spectroscopies. The NCD-coated QCM gas sensors showed a reasonable performance with a stable repeatability to the tested gases. The response time of the tested diamond-coated sensor was fast (∼5 s). Moreover, we also observed higher sensitivity and better stability for NCD-coated QCM than for the bare QCM.

Use of a Quartz Crystal Microbalance for Studying the Effects of Propyl Gallate on the Interactions of Interleukin-6 and Its Soluble Receptor

Quartz Crystal Microbalance (QCM) is known as a surface sensitive analytical device capable of on-line monitoring of interfacial reactions. To study the interaction between interleukin-6 (IL-6) and its soluble receptor (sIL-6R), as well as the effects of propyl gallate on IL-6/sIL-6R binding based on it, a QCM was employed to monitor the binding responses. In the experiments, sIL-6R was immobilized on the surface of QCM substrate, then different concentrations of IL-6 were added onto the substrate, respectively. The response frequency shift caused by the binding between IL-6 and sIL-6R was recorded. The results showed that sIL-6R was immobilized on the substrate surface with the density of 3.43 ng/mm2, IL-6 then bound to the immobilized sIL-6R specifically. FAST fit program was used to analyse the data obtained of the association of IL-6 and immobilized sIL-6R, fitting it to the biphasic kinetic equations. Kinetic constantsfor IL-6 binding to sIL-6R were determined from the plots of Kon versus the concentration of IL-6, kass=3.41×104 M-1 s-1, kdiss=1.80×10-2 s-1, thus, KD=5.28×10-7 M, KA=1.89×106 M-1. Furthermore, the effects of propyl gallate (PG) on interaction of IL-6 with sIL-6R were studied. The results showed that PG was able to enhance the binding between IL-6 and sIL- 6R. We propose that the interaction between IL-6 and sIL-6R is one of the targets which PG can act on in vivo. The QCM offers an effective way and a new clue to the study on the mechanism of propyl gallate at molecular level.

Nanorheology of liquid crystal thin films confined between interfaces with anisotropic molecular orientations

The hydrodynamic properties of confined liquids play a significant role in the transportation of fluids in microfluidics, nanofluidics, and flows in porous media so on. In this paper, the effective viscosities of 4-Cyano-4′-pentyl biphenyl (5CB) liquid crystals (LCs) confined in a slab geometry with interfaces of anisotropically oriented molecules were investigated by a quartz crystal microbalance (QCM). A novel nanocell was fabricated onto the QCM substrate chip resulting in a 520-nm-thick slab geometry for viscosity measurement. Rubbed polyimide layer was spinning coated onto the nanocell interfaces to obtain different combinations of interfacial molecular orientations of the added 5CB LCs. The resulted effective viscosity of 5CB LCs increased by ~14 % on the interface with LC molecules oriented vertically to the shearing direction. However, it decreased on the substrate interface with LC molecules parallel along the shearing direction and decreased up to ~58 % when the LCs was confined in the nanocell with both parallel oriented interfaces. A varying magnitude of ~300 % in LC effective viscosity could be obtained by tailoring the interfacial molecular orientations. We also demonstrated that the shear resistance applied on the interface is predominated by the liquid microstructure within nanometers distance from the wall, but weakly influenced by that far from the local interface. The results were analyzed in terms of LC intermolecular friction and the predominance of the interfacial molecules at nanoscale, which are of the utmost importance for fluid transportation in microfluidics, in porous media, or in boundary lubrications.

Temperature effect on template polymerization of methacrylic acid using stereocomplex formation on quartz crystal microbalance substrates

ABSTRACTThe radical polymerization of methacrylic acid (MAA) at 0, 20, 40, and 70 °C was achieved in porous isotactic (it‐) poly(methyl methacrylate) (PMMA) films on quartz crystal microbalance (QCM) substrates, which were prepared by layer‐by‐layer assembled stereocomplex films of it‐PMMA and syndiotactic (st‐) poly(methacrylic acid) (PMAA), followed by the subsequent extraction of st‐PMAA. The MAA polymerization yields increased from 35 to 75%, as the polymerization temperature increased from 0 to 70 °C. Furthermore, infrared spectroscopy revealed that a higher polymerization temperature is necessary to form it‐PMMA/st‐PMAA stereocomplexes via stereoregular polymerization manner that resemble native it‐PMMA/st‐PMAA stereocomplexes. X‐ray diffraction pattern of porous it‐PMMA were also investigated for reaction fields. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3032–3036