Efficient Synthesis of Narrowly Dispersed Brush Copolymers and Study of Their Assemblies: The Importance of Side Chain Arrangement

Efficient, one-pot preparation of synthetically challenging, high molecular weight (MW), narrowly dispersed brush block copolymers and random copolymers in high conversions was achieved by ring-opening metathesis (co)polymerization (ROMP) of various macromonomers (MMs) using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H_2IMes)(pyr)_2(Cl)_2RuCHPh. A series of random and block copolymers were prepared from a pair of MMs containing polylactide (PLA) and poly(n-butyl acrylate) (PnBA) side chains at similar MWs. Their self-assembly in the melt state was studied by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). In brush random copolymers containing approximately equal volume fractions of PLA and PnBA, the side chains segregate into lamellae with domain spacing of 14 nm as measured by SAXS, which was in good agreement with the lamellar thickness measured by AFM. The domain spacings and order−disorder transition temperatures of brush random copolymers were insensitive to the backbone length. In contrast, brush block copolymers containing approximately equal volume fractions of these MMs self-assembled into highly ordered lamellae with domain spacing over 100 nm. Their assemblies suggested that the brush block copolymer backbone adopted an extended conformation in the ordered state

The influence of the clay particles on the mechanical properties and fracture behavior of PLA/o-MMT composite films

In this study, calendered films of polylactic acid/organo-montmorillonite clay (PLA/o-MMT) were prepared and the influence of the clay particles' morphology on the mechanical properties and fracture behavior was evaluated. An image analysis was performed using transmission electron microscopy micrographs to complete the morphological study. The micrographs were taken from ultramicrotomic samples corresponding to the melting flow (MD) and transverse direction (TD) of the films. The micrographs revealed intercalated particles and tactoids, which were in accordance with the wide angle X-ray scattering patterns. Uniaxial tensile tests were performed in the MD and TD directions, finding a slight anisotropy in the films, which was associated with a low level of polymer chain orientation due to the calender processing. The fracture behavior was also evaluated in the MD and TD directions using deeply double-edge-notched tension (DDENT) specimens. The mechanical and fracture tests were evaluated on aging (brittle) and deaging (ductile) films by applying a thermal treatment that consisted of heating above the glass transition temperature of the PLA and subsequent quenching. For ductile PLA composite films, the reinforcement effect promoted by the clay particles was not so evident.Peer ReviewedPostprint (author’s final draft

Predicting the strength of 3D-printed conductive composite under tensile load: A probabilistic modeling and experimental study

Conductive PLA is an innovative composite material that combines the ecological benefits of polylactic acid, a biodegradable thermoplastic, with electrical conductivity properties. Usually used in additive manufacturing for its ease of printing and low environmental impact, PLA remains an insulator, which limits its applications in the electrical field. To overcome this limitation, conductive fillers such as carbon nanotubes or carbon black are being added, opening the way to new functional uses. This study focuses on a specific composite: carbon black-filled PLA (PLA-CB). This material combines the qualities of traditional PLA with enhanced conductivity thanks to the carbon black particles. To assess its performance, a number of mechanical tests were carried out, including tensile tests on samples manufactured by 3D printing using the FFF process. The study focused in particular on the influence of crosshead speed and the impact of different notch shapes on the material's properties. To analyze the durability of PLA-CB, a probabilistic model based on the two-parameter Weibull distribution was used to assess the risk of failure under different conditions. Reliability curves were also established to better understand the tensile stress and strain at break of the material. This approach could also be applied to other 3D-printed polymers to refine their analytical and numerical modeling

4D Printing of Commercial Based Conductive Polylactic Acid: Strength and Resistance Properties

Four-dimensional (4D) printing technology is an innovative concept integrating conventional 3D printing additive manufacturing (AM) and smart materials programed to change properties or shape over time in response to environmental stimuli. This study aims to characterize the strength and electrical resistance of a commercial electrically conductive polylactic acid (PLA) with carbon black (CB) particles printed by fused filament fabrication (FFF) technique to evaluate the development feasibility of two sensor prototypes: (1) a load-cell sensor, and (2) a temperature sensor. Experiments were performed to study the orientation and raster angle–dependent mechanical and electrical performance of a PLA-CB conductive polymer manufactured by AM-FFF technology. A good agreement was observed between the data received from the manufacturer and the experimental density of the conductive AM-FFF PLA-CB three-point bending samples. The mechanical properties of 3D-printed PLA-CB were characterized based on three-point bending flexural test. Two build orientations (flat and upright) and three raster patterns (0°/90°, +45°/-45°, and concentric) were printed to check the optimal mechanical properties for electrical conductivity; six samples were printed for each one of the six configurations. The three-point bending flexural test results of the examined 36 specimens demonstrated that the samples printed in the concentric and +45°/-45° raster patterns exhibit the best mechanical properties, with the highest flexural strength and flexural modulus of elasticity in the flat orientation. Nevertheless, the concentric pattern has an advantage over the +45°/-45° pattern due to higher density and homogeneity. To examine the electrical resistance of the PLA-CB material another 12 specimens were printed and divided into four groups, each with different lengths. The electrical intrinsic resistivity was calculated from the geometry of the specimens and the measured resistance, with an average value of 13.2 [Ω·cm]. To check the production feasibility of a load-cell sensor prototype the effect of load on electrical conductivity was examined, however no effect of load on resistance was discovered. To prove the production feasibility of a sensor prototype for temperature measurements a preliminary device was designed and the effect of increasing and decreasing the temperature between 24 and 42°C on electrical resistance was examined. Based on the experimental results a calibration function was built linking between the temperature and the material’s resistance

Predicting the strength of 3D-printed conductive composite under tensile load: A probabilistic modeling and experimental study

Conductive PLA is an innovative composite material that combines the ecological benefits of polylactic acid, a biodegradable thermoplastic, with electrical conductivity properties. Usually used in additive manufacturing for its ease of printing and low environmental impact, PLA remains an insulator, which limits its applications in the electrical field. To overcome this limitation, conductive fillers such as carbon nanotubes or carbon black are being added, opening the way to new functional uses. This study focuses on a specific composite: carbon black-filled PLA (PLA-CB). This material combines the qualities of traditional PLA with enhanced conductivity thanks to the carbon black particles. To assess its performance, a number of mechanical tests were carried out, including tensile tests on samples manufactured by 3D printing using the FFF process. The study focused in particular on the influence of crosshead speed and the impact of different notch shapes on the material's properties. To analyze the durability of PLA-CB, a probabilistic model based on the two-parameter Weibull distribution was used to assess the risk of failure under different conditions. Reliability curves were also established to better understand the tensile stress and strain at break of the material. This approach could also be applied to other 3D-printed polymers to refine their analytical and numerical modeling

Design and development of low-cost rapid prototyping approaches for electrochemical microfluidic sensing

El objetivo principal de esta Tesis Doctoral ha sido diseñar, desarrollar y validar dispositivos electroquímicos microfluídicos empleando técnicas de prototipado rápido y de bajo coste que puedan ser implementadas en laboratorios convencionales por usuarios que no cuenten con experiencia previa en microfabricación. En un primer bloque se diseñaron y desarrollaron dispositivos basados en xurografía para la microfluídica, serigrafía para los electrodos y laminación térmica para el montaje final de los dispositivos. En primer lugar, se estudió la transferencia de nanomateriales filtrados en membrana mediante laminación térmica para la construcción de electrodos basados exclusivamente en nanomateriales de carbono. Se estudiaron las condiciones óptimas de preparación, y aquella con las mejores prestaciones analíticas se integró en una celda electroquímica serigrafiada para la determinación de L-tirosina en muestras clínicas de tirosinemia tipo I. Seguidamente, se exploró la construcción de dispositivos electroquímicos microfluídicos constituidos por electrodos serigrafiados, lo cual dificulta la adhesión de la capa microfluídica debido al elevado grosor de estos electrodos. Este problema se solventó mediante la construcción de dispositivos de varias capas de plástico que finalmente se unen por laminación térmica. En primer lugar, se demostró la presencia del régimen laminar propio de los sistemas microfluídicos y que la corriente amperométrica límite sigue el modelo de Levich. Finalmente, para poner de manifiesto la versatilidad y el potencial de esta técnica, se diseñaron dispositivos microfluídicos de doble canal con sendas células electroquímicas integradas para llevar a cabo ensayos simultáneos e independientes de capacidad antioxidante. En un segundo bloque, se optó por emplear impresión 3D, más concretamente fabricación por filamento fundido, como un avance tecnológico para la fabricación de estos dispositivos debido a que permite la automatización del proceso y permite de forma secuencial la fabricación de la microfluídica, la deposición de los electrodos y el ensamblaje del dispositivo final. En primer lugar, se estudió la construcción de los dispositivos electroquímicos microfluídicos y distintos métodos (electro)químicos de activación para los electrodos de carbono impresos 3D que no poseen prestaciones electroquímicas idóneas recién impresos. Se demostró que la activación mediante voltamperometría cíclica en medio alcalino daba los mejores resultados y seguía el modelo de Levich. Estos dispositivos se emplearon para la determinación de dopamina en medio celular fortificado. Posteriormente, y aprovechando la funcionalidad de impresión-pausa-impresión de la impresión en 3D se propuso una fabricación alternativa de los dispositivos electroquímicos microfluídicos para evitar la activación tras la impresión de los electrodos. Para ello, tras depositar los electrodos impresos en 3D se pausó la impresión y se modificaron secuencialmente con tintas conductoras de carbono (electrodo de trabajo y auxiliar) y Ag/AgCl (electrodo de referencia), con Prussian Blue mediante electrodeposición y drop-casting, y finalmente con glucosa oxidasa para construir un biosensor amperométrico de glucosa de primera generación. Finalmente, se exploró el método de arco eléctrico para la activación de electrodos impresos en 3D de forma automática y que ulteriormente puede ser integrado en el flujo de trabajo de la impresión 3D. Mediante esta técnica se depositan nanoestructuras de carbono en los electrodos provenientes de grafito mediante la aplicación de voltajes elevados (~1 kV DC). La modificación de estos electrodos se caracterizó tanto morfológica como espectroscópicamente y su desempeño electroquímico se estudió en función del número de capas de electrodo impresas. Los electrodos con mejor desempeño electroquímico se empelaron para la determinación voltamperométrica simultánea de dopamina y serotonina en medio celular fortificado. Por todo ello, en esta Tesis Doctoral se ha demostrado que las técnicas de prototipado rápido constituyen una herramienta con enorme potencial para el desarrollo de sistemas microfluídicos electroquímicos con elevadas prestaciones analíticas

MANUFACTURING AND CHARACTERIZATION OF POLY (LACTIC ACID)/CARBON BLACK CONDUCTIVE COMPOSITES FOR FDM FEEDSTOCK: AN EXPLORATORY STUDY

This exploratory study developed methods of manufacturing and characterizing the electrical properties of small batches of conductive composite feedstock for the Fused Deposition Modeling (FDM) manufacturing process, commonly known as 3D printing. We utilized a solution casting process of Poly(lactic acid) (PLA) (Grade 4043D, NatureWorks, LLC.) and Carbon Black (CB) (Vulcan® XC72, Cabot Corp.) in chloroform. The resulting composite precursor was cryogenically treated with liquid nitrogen and milled in a coffee grinder in order to achieve particles that could be fed into the extruder. Composite precursors were dried in a vacuum oven at an elevated temperature of 38°C. Filaments were produced via filament extruder (Filastruder 2.0). Volume resistivity was measured using a modified method of ASTM D991-89 with a customized test fixture. Compositions ranging from 0.1 to 45 vol% of CB were manufactured in this way. Results indicated that compositions of 25 vol% and 30 vol% CB showed regions of conductivity in the filament, however their conductivities were highly inconsistent, with lengths of filament having both conductive and nonconductive regions. Regions that did conduct were ohmic, with volume resistivities ranging from 1.4 to 63 * 10-2 ohm*m. Samples with concentrations of 35 vol% and greater were unable to be extruded effectively due to the limitations of the equipment available

Volumetric characterization of the nano- and microconfiguration of nanocomposites with conductive fillers by dielectric spectroscopy

Ein Effektiv-Medium-Modell (Polder/van Santen/Böttcher-Modell oder PvSB-Modell) wurde verwendet, um die dielektrischen Eigenschaften von Verbundwerkstoffen in Abhängigkeit von ihrer Füllstoffdispersion und -orientierung zu beschreiben. Das Modell wurde experimentell anhand von Referenzproben mit definiert eingestellter Dispersion und Orientierung der Füllstoffe validiert. Neben der Verwendung des PvSB-Modells, wurde zur Simulation der dielektrischen Eigenschaften von Verbundwerkstoffen die Finite-Elemente-Methode (FEM) angewandt. Bei geringen Füllstoffkonzentrationen stimmen die Ergebnisse von Simulation und Modell sehr gut überein. Bei hohen Konzentrationen beginnen die Ergebnisse voneinander abzuweichen. Die vom PvSB Modell nicht berücksichtigten Parameter, wie der relative Abstand zwischen den Füllstoffen oder die Netzwerkbildung von Füllstoffen, wurden mit Hilfe der FEM simuliert. Es wurde festgestellt, dass die meisten dieser Parameter einen vernachlässigbaren Einfluss auf die Gesamtpermittivität des Komposits haben. Lediglich die Netzwerkbildung der Füllstoffe führte zu einem erheblichen Effekt. Eine Erweiterung des PvSB-Modells (e-PvSB) wurde folglich vorgeschlagen, um die Kontakt- oder Netzwerkbildung der Füllstoffe in einem Komposit zu berücksichtigen. Zu diesem Zweck wurde ein neuer Parameter definiert, der Netzwerkfaktor. Darauf aufbauend wurde eine Methode zur Verwendung des e-PvSB-Modells vorgeschlagen, um morphologische Informationen aus experimentellen Daten zu erhalten. Die Methode wurde angewandt, um anhand von Messdaten der Permittivität, die Morphologie von Polymer- Nanokompositen mit Kohlenstoff-Nanoröhren und Ruß unter verschiedenen Zuständen von Dispersion und Ausrichtung abzuschätzen

Experimentación de las capacidades de filamentos termoplásticos en la fabricación aditiva FDM para crear objetos interactivos

La fabricación aditiva FDM de escritorio se presenta como una técnica prometedora para la integración de componentes electrónicos pasivos con morfologías orgánicas. En este trabajo, se exploró la creación de sensores capacitivos utilizando filamento conductor PLA/CB mediante FDM. Para optimizar la calidad superficial y la conductividad del filamento, se realizó una experimentación con la configuración de impresión: temperatura de cama, temperatura de boquilla, enfriamiento, flujo, velocidad de impresión y longitud de retracción. Además, se optimizaron la configuración de relleno, la orientación de deposición del filamento y la altura de capa. Los resultados muestran una mejora significativa en la calidad superficial de las piezas impresas, validando esta tecnología para la impresión de sensores capacitivos.Licenciatura en Diseño de Producto

고분자 유도 카본블랙 구조체가 형성된 폴리락틱산 복합체의 전기적 및 유변학적 거동에 관한 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 화학생물공학부, 2021.8. 안경현.The goal of this thesis is to examine the aggregation and percolation of carbon black (CB) particles in poly(lactic acid) (PLA) matrix through the addition of poly(caprolactone) (PCL) or thermoplastic polyurethane (TPU) as a secondary polymer and to investigate its effect on the rheological, electrical and mechanical properties of the composites depending on mixing protocol and the concentration or variation of secondary polymers. The electrical conductivity of ternary composites composed of a biopolymer blend with conductive CB particles is increased by the control of particle dispersion in the dispersed phase. As the CB particles have higher chemical affinity for the secondary PCL phase than the PLA matrix, especially when the concentration of the PCL decreases to 4 wt%, the PCL phase induces the aggregation of CB particles, resulting in a shift of the particle percolation threshold to a lower concentration of particles (3.73 vs. 2.86 wt% CB). Moreover, the mixing ratio between the CB and the PCL significantly affects the formation of CB dispersion structure. Image analysis confirms that the addition of a small amount of PCL induces the formation of particle aggregates with a high aspect ratio, providing direct 3D conducting pathways due to the multiple contact points between the particle aggregates (power law scaling exponent of the composites decreases to ~2.2). Meanwhile, in order to design an electrically conductive and ductile PLA composite, this thesis also examines the effect of the addition of a small amount of various secondary polymers with a different chemical affinity to CB particles at a fixed blending process on the structural change of CB. The electrical conductivity of ternary composites increases by 3-4 orders of magnitude higher than the binary PLA/CB composite, while TPU-added composite increases ductility up to 220 % with only 4 wt% CB and 4 wt% secondary polymer. Fractal analysis shows that the CB particles in the PCL or TPU-added ternary composites aggregate through diffusion-limited cluster aggregation process (fractal dimension ~1.8), leading to a ductility improvement due to good CB-secondary polymer adhesion strength. Moreover, the TPU-added composite forms larger CB aggregates than PCL-added composite due to higher interaction between CB and TPU than that of PCL, leading to further improved ductility. Next, to further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with PCL-induced CB aggregation in the form of a large aspect ratio and large aggregates (aggregate perimeter ~ aggregate size0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher-order structure (aggregate perimeter ~ aggregate size0.8). The reduced size of the PCL phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The electrical conductivity of the ternary composite with the higher-order structure is remarkably enhanced to 4x10-2 S/m with 4 wt% CB. This thesis provides optimal process and chemical condition for fabricating polymer-induced particle aggregates in order to realize the electrically conductive and ductile biopolymer composites.본 논문에서는 소량의 폴리카프로락톤 및 열가소성 폴리우레탄을 제 2상 고분자로 첨가하였을 때 폴리락틱산 매트릭스 내에서 카본블랙 입자의 응집과 퍼콜레이션 현상에 대해서 알아보았고, 용융-혼합 방법과 각 재료의 농도에 따른 카본블랙 응집체의 구조와 복합체의 물성과의 상관관계를 규명하였다. 카본블랙 입자와 생분해성 고분자 블렌드로 구성된 3상 복합체의 전기 전도도는 분산상 고분자 존재 하에서 입자의 분산을 제어함으로서 증가시킬 수 있었다. 카본블랙 입자가 폴리락틱산 매트릭스 고분자보다 제 2상 고분자인 폴리카프로락톤에 더 높은 화학적 친화성을 갖는 경우, 폴리카프로락톤의 농도가 4 wt%로 감소함에 따라 폴리카프로락톤 상은 카본블랙 입자의 응집을 유도하였으며, 이로 인해 퍼콜레이션 임계 값이 더 낮은 농도로 이동하였음을 확인하였다 (3.73 vs. 2.86 wt%). 또한, 카본블랙과 폴리카프로락톤 상의 혼합 비율은 카본블랙의 분산 구조 형성에 큰 영향을 미치는 것을 확인하였다. 이미지 분석을 통해, 소량의 폴리카프로락톤 상의 첨가는 높은 종횡비를 갖는 입자 응집체를 형성시켰으며, 이러한 입자 응집체 간의 다중 접촉으로 인해 직접적인 3차원 전자 전달 경로가 형성되는 것을 확인하였다 (복합체의 멱함수 지수가 2.2로 감소). 한편, 전기 전도성 및 고 연성 폴리락틱산 복합체를 설계하기 위해, 본 논문에서는 다양한 제 2상 고분자를 사용함으로 카본블랙과 제 2상 고분자의 화학적 친화성을 제어하였고, 이로 인한 카본블랙 응집체의 구조적 변화를 분석하였다. 폴리카프로락톤 및 열가소성 폴리우레탄이 첨가된 3상 복합체의 전기 전도도는 2상 복합체인 폴리락틱산/카본블랙 복합체보다 103-104배 더 높은 것이 확인되었고, 특히 열가소성 폴리우레탄이 첨가된 3상 복합체의 연신율은 4 wt%의 카본블랙과 4 wt%의 열가소성 폴리우레탄이 첨가되었을 때 220 % 증가한 것이 확인되었다. 프랙탈 구조 분석을 통해, 폴리카프로락톤 또는 열가소성 폴리우레탄이 첨가된 3상 복합체 내에서의 카본블랙 응집체의 응집 과정이 확산-제한적 응집 과정임을 (프랙탈 지수 1.8) 규명할 수 있었으며, 이를 통해 제 2상 고분자와 카본블랙 입자 사이의 강한 접착 강도로 인해 연성이 향상되었다는 사실을 확인할 수 있었다. 또한, 열가소성 폴리우레탄이 첨가된 복합체는 폴리카프로락톤 보다 카본블랙과 제 2상 고분자 사이의 상호 작용이 더 크기 때문에, 더욱 큰 크기의 카본블랙 응집체를 형성하여 연성을 더욱 향상시켰다. 또한, 본 논문에서는 퍼콜레이션 구조를 제어하기 위해서, 복합체의 제조 방법을 전형적인 1단계 혼합 과정에서 2단계 혼합 과정으로 분할하여 제 2상 고분자인 폴리카프로락톤 상과 카본블랙 입자의 분산을 각각 조절하였다. 카본블랙 입자와 폴리카프로락톤 상의 함량이 4 wt%로 고정되었을 때, 1단계 혼합 공정으로 제조된 3상 복합체에는 유도 입자 응집 현상으로 인해 비교적 높은 종횡비와 큰 크기의 응집체가 형성된 것이 확인되었다 (응집체의 둘레~응집체의 직경0.7). 반면, 2단계 혼합 공정으로 제조된 복합체에는 카본블랙 응집체가 확장된 고차원 구조가 형성된 것이 확인되었다 (응집체의 둘레~응집체의 직경0.8). 카본블랙 입자가 첨가되기 전, 높은 전단력을 가진 첫 번째 혼합 단계에서 폴리카프로락톤 상의 크기의 감소는 카본블랙 입자가 후속 혼합 단계에서 카프로락톤 상과 접촉할 수 있는 더욱 큰 계면 영역을 제공하였으며, 결과적으로 복합체 전체에 걸쳐 확장된 카본블랙 응집체를 형성시켜 주었다. 그 결과, 고차원의 구조를 갖는 3상 복합체의 전기 전도도는 카본블랙 4 wt% 농도에서 4x10-2 S/m로 현저하게 향상되었다. 복합체의 물성과 제 2상 고분자 첨가에 의해 형성된 카본블랙 유도 응집체의 구조적 상관관계를 조사한 본 논문은 전기 전도성 및 고 연성 생분해성 고분자 복합체를 실현하기 위한 최적의 공정 및 화학적 조건을 제공한다.Chapter 1. Introduction 1 1.1. General introduction 2 1.2. Overview of thesis 7 Chapter 2. Background 9 2.1. Conductive biopolymer composites 10 2.2. Fabrication of conducting network : double percolation 13 2.3. Fabrication of conducting network : polymer induced aggregation 17 2.4. Objectives of thesis 22 Chapter 3. Experimental methods 23 3.1. Sample preparation 24 3.2. Visualization and image analysis 30 3.3. Property characterization of composites 32 Chapter 4. Results and discussion 34 4.1. Composition dependent structural changes 35 4.1.1. Morphology development 35 4.1.2. DC conductivity and rheological properties 41 4.1.3. Electrical and rheological percolation analysis 48 4.2 Polymer/particle interaction dependent structural changes 55 4.2.1. Morphology development 55 4.2.2. Fractal analysis of CB aggregates 65 4.2.3. Electrical, mechanical and rheological properties 73 4.3 Mixing protocol dependent structural changes 88 4.3.1. Morphological and electrical properties 88 4.3.2. Electrical and rheological characterization 106 4.4 Discussion 114 Chapter 5. Summary 117 국문 초록 121 References 124박