A concept inventory for knowledge base evaluation and continuous curriculum improvement

Students at Polytechnique Montreal have demonstrated the ability to tackle large-scale, complex calculations through their integrative projects. However, high quality engineers must not only master calculations, but the underlying fundamental concepts as well — this level of retention allows them to transfer their knowledge to the new challenges they will face. To ensure this, accreditation criteria for engineering programs in Canada require the evaluation of multiple attributes, the first of which is “a knowledge base for engineering”. While most universities opt to evaluate this attribute through in-class grades, we choose to adapt a pedagogical tool (a concept inventory) to formulate an evaluation of our students. Our students are examined using a subset of questions from more than 800 chemical engineering questions, split into 10 subcategories. Data amassed over four years is presented, showing the impact of various improvements to this tool, as well as its use for instructor feedback and curriculum improvement. Key improvements include question revisions and targeted reviews of muddy concepts in the affected courses

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration

The structural amphiphilicity of cellulose nanocrystals characterized from their cohesion parameters

Cellulose nanocrystals (CNCs), usually considered as isotropically polar nanoparticles, are sheet-like crystalline assemblies of cellulose chains. Here, we link the anisotropy of the CNC structure to an amphiphilic behavior in suspension. The Hansen solubility parameters (HSP: δD; δP; δH) of woodbased H2SO4-hydrolyzed CNCs were measured from sedimentation tests in a wide set of 59 solvents and binary mixtures. Two sets of cohesion parameters corresponding to a polar surface (18.1; 20.4; 15.3) ± (0.5; 0.5; 0.4) MPa1/2 and to a mildly non-polar one (17.4; 4.8; 6.5) ± (0.3; 0.5; 0.6) MPa1/2 were determined, with respective solubility radii of 7.8 and 2.1MPa1/2. The polar sphere is thought to correspond to the (110)&(110) surfaces of cellulose Iβ nanocrystals, while the smaller non-polar sphere is coherent with the exposure of (200) surfaces. The HSP graph provides new insights on the amphiphilic nature of CNCs and a mapping of their chemical affnity for solvents and polymer matrices

VUV Photodeposition of Thiol-Terminated Films: A Wavelength-Dependent Study

Photoinitiated chemical vapor deposition (PICVD) has become attractive for selective and specific surface functionalization, because it relies on a single energy source, the photons, to carry out (photo-) chemistry. In the present wavelength (λ)-dependent study, thiol (SH)-terminated thin film deposits have been prepared from gas mixtures of acetylene (C2H2) and hydrogen sulfide (H2S) via PICVD using four different vacuum-ultraviolet (VUV) sources, namely, KrL (λpeak = 123.6 nm), XeL (λpeak = 147.0 nm), XeE (λpeak = 172.0 nm), and Hg (λ = 184.9 nm) lamps. Different λ influence the deposition kinetics and film composition, reflecting that photolytic reactions are governed by the gases’ absorption coefficients, k(λ). Thiol concentrations, [SH], up to ∼7.7%, were obtained with the XeL source, the highest reported in the literature so far. Furthermore, all films showed islandlike surface morphology, regardless of λ

Polyethylene glycol and poly(vinyl alcohol) hydrogels treated with photo-initiated chemical vapor deposition

Résumé: La présente étude a été conçue en vue de déterminer si une modification de la surface par PICVD (dépôt chimique en phase vapeur photo-initié) a une incidence différente sur les propriétés physicochimiques du polyéthylèneglycol (PEG) que sur celles du polyvinylalcool (PVA), étant donné leur structure et leurs propriétés chimiques différentes. Les mesures de l’angle de contact ont révélé une augmentation de l’hydrophobicité de la surface des deux polymères après un traitement par PICVD. De plus, l’accroissement de l’hydrophobicité a facilité la dispersion dans les solvants non polaires. Les changements chimiques étaient concentrés près de la surface, comme en témoignent les mesures de spectroscopie infrarouge à transformée de Fourier (FTIR) et de spectroscopie de photoélectrons X (XPS), qui indiquent notamment qu’une oxydation partielle se produit au cours du traitement. Nous discutons de ces résultats du point de vue des différences entre les structures moléculaires du PEG et du PVA, lesquelles modulent la fonctionnalisation et l’hydrophobicité de leur surface. ---------- Abstract: This study was designed to determine if surface modification via photo-initiated chemical vapor deposition (PICVD) affects the physicochemical properties of polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA) differently, given their different chemical structures and properties. Contact angle measurements showed that both polymers increase in surface hydrophobicity after PICVD treatment. Further, the improved hydrophobicity facilitated dispersion into nonpolar solvents. Chemical changes were concentrated near the surface, evidenced by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements, indicating namely that partial oxidation occurs during treatment. These findings were discussed in the context of the difference of the molecular structures of PEG and PVA, which, in turn, control their surface functionalization and hydrophobicity

Photo-initiated chemical vapor deposition as a scalable particle functionalization technology (a practical review)

ABSTRACT: Chemical vapor deposition (CVD), and its variants, is a more viable technology than the addition of surface active agents to modify nanoparticle surfaces. While thermally-activated CVD simply works by initiating the monomers using heat, some other techniques are more powerful and versatile. Indeed, higher energy CVD methods open up possibilities to a wider range of monomers. Unfortunately, different terminologies and classifications due to parallel work have led to confusion. This paper presents and explains the different techniques as well as their equivalent terminologies to clarify the big picture. While the demand for functionalized nanoparticles grows rapidly, current functionalization methods are still too expensive for most applications. This paper is intended to be a practical review of the gas phase methods available in order to identify a potential candidate for large scale functionalization of nanoparticles. This study identifies photo-initiated CVD (PICVD) as an ideal solution for scalable particle functionalization technology

Resistance welding of thermoplastic composites with a nanocomposite heating element

In this study, we propose a new heating element (HE) for the resistance welding of thermoplastic composites. This HE is made of polyetherimide (PEI), rendered electrically conductive by the addition of 10% wt. multi-wall carbon nanotubes (MWCNT) (conductivity of 0.79 S cm-1). The new HE was successfully used to weld carbon fibre/poly (ether ketone) (CF/PEEK) laminates in a single lap shear configuration, leading to a lap shear strength of up to 19.6 MPa. Observations of the fracture surfaces revealed a cohesive failure mode within the nanocomposite HE and non-uniform heating over the weld area. It is believed that PEI/MWCNT HE present an interesting alternative to current HE, although more work is needed to improve the temperature homogeneity over the weld area

The apparent structural hydrophobicity of cellulose nanocrystals

The Teas graph of wood-based sulfuric acid-hydrolyzed cellulose nanocrystals (CNCs) was plotted based on sedimentation tests in a set of 25 common solvents. Comparisons with those of sucrose and dextran, taken as equivalents for cellobiose (cellulose repeating unit) and amorphous cellulose, respectively, highlighted the amphiphilic nature of CNCs. In the absence of any chemical arguments, the hydrophobic behavior displayed is thought to be caused by the exposition of (200) lattice planes at the CNC surface. This apparent structural hydrophobicity may be exploited to achieve the dispersion of CNCs in some mildly-non polar matrices such as poly(ethylene glycol) and poly(lactic acid). The Teas graph is a useful tool to predict the dispersibility potential of CNCs and to select a proper solvent for nanocomposite preparatio

Tailoring cellulose nanocrystals rheological behavior in aqueous suspensions through surface functionalization with polyethyleneimine

The present paper reports the surface modification of commercially available cellulose nanocrystals (CNCs) using polyethyleneimine (PEI) by means of non-covalent electrostatic interaction between the negatively charged sulfate groups of CNCs and positively charged amine functionalities of PEI. The modification, carried out in an aqueous medium, results in a stable CNC-PEI suspension with no phase separation that exhibit interesting rheological behavior due to bridging-type inter-particle interactions. The Newtonian 3% (w/w) CNC suspension evolves into a non-Newtonian gel system after modification with PEI with a consequent increase of almost three decades in complex viscosity. Preshearing of the 3% (w/w) CNC-PEI suspension resulted in the loss of the linear viscoelastic properties with increasing shear rate, as would be expected from the breaking of the inter-particle network. However, the system gradually re-established the inter-particle network in less than an hour to give the original rheological parameters. The effect of PEI on the rheological properties was attributed to the physical adsorption of PEI chains on the CNC particles, examined by dynamic light scattering (DLS), zeta potential, X-ray photoelectron spectroscopy (XPS), elemental analyses, and isothermal adsorption studies. The modified CNC-PEI particles did not show any significant change in the particle morphology compared to the unmodified CNCs, as observed from transmission electron microscope (TEM) images

Continuous aerosol photopolymerization to coat de-agglomerated nanoparticles

A novel continuous aerosol photopolymerization technique to coat nanoparticles that have been previously de-agglomerated is presented. After de-agglomeration in a jet-impactor assisted fluidized bed, monomer vapors are condensed onto the surface of aerosol nanoparticles via heterogeneous condensation. Photopolymerization is initiated through exposure to UV light. To demonstrate the process, titanium dioxide (TiO2) and methyl methacrylate (MMA) were selected as nanoparticle and organic monomer, respectively. We demonstrated this light-based technique, operated at ambient pressure and room temperature, is able to graft a PMMA-like film with a thickness of 1.5 nm on the surface of nanoparticles, confirmed by TEM and FTIR. XPS analysis confirmed formation of covalent bonds with the TiO2 surface, indicating a surface-initiated photopolymerization. Particle size measurements in suspension state illustrated the efficiency of the de-agglomeration and subsequent coating process, as coated particles remained smaller than bare particles. UV-Vis absorbance spectra show that the coating facilitates dispersion in non-polar solvents. Finally, long-term stability experiment confirmed the suspension stability is enhanced not only because of the reduction of agglomerate sizes, but also as a result of the carbon coating which improves the interfacial interactions between particleparticle and particle-solvent. This technique can be easily combined with any continuous inorganic nanoparticle synthesis processes as a solvent-free post-synthesis process to impart a functional coating