Hydration and Viscoelastic Properties of High- and Low-Density Polymer Brushes Using a Quartz-Crystal Microbalance Based on Admittance Analysis (QCM-A)

Threshold of Surface Initiator Concentration for Polymer Brush Growth by Surface-Initiated Atom Transfer Radical Polymerization

The surface modification of various materials by grafting functional molecules has attracted much attention from fundamental research to practical applications because of its ability to impart various physical and chemical properties to the surfaces. One promising approach is the use of polymer brushes synthesized by atom transfer radical polymerization (ATRP) from surface-tethered initiators (SIs). In this study, for the purpose of controlling the grafting amounts/densities of polymer brushes, we developed a facile method to precisely regulate SI concentrations of SI layers (SILs) by serial dilution based on a sol-gel method. By simply mixing organosilanes terminated with and without an initiator group ((p-chloromethyl) phenyltrimethoxysilane (CMPTMS) and phenyltrimethoxysilane (PTMS), respectively) with tetraethoxysilane (TEOS), SI concentrations of SILs could be arbitrarily tuned precisely by varying dilution factors of (CMPTMS + PTMS)/CMPTMS (DFs, 1-107). The resulting SILs prepared at different DFs were highly smooth and transparent. X-ray photoelectron spectroscopy (XPS) also confirmed that the SIs were homogeneously distributed at the topmost surface of the SILs and their concentrations were proven to be accurately and precisely controlled from high to extremely low, comparable to theoretical values. Subsequent SI-ATRP in air ("paint-on" SI-ATRP) of two different types of monomers (hydrophobic/nonionic (2,3,4,5,6-pentafluorostyrene) and hydrophilic/ionic (sodium 4-styrenesulfonate)) demonstrated that polymer brushes with different grafting amounts/densities were successfully grafted only from SILs with DFs of 1-104 (theoretical SI concentrations: 3.9 × 10-4 ∼ 3.5 units/nm2), while at DFs of 105 and above (theoretical SI concentrations: <3.9 × 10-5 units/nm2), no sign of polymer brush growth was confirmed by thickness, XPS, and water contact angle data. Therefore, we are the first to gather evidence that the approximate threshold of SI concentration required for "paint-on" SI-ATRP might be on the order of 10-4 ∼ 10-5 units/nm2.

Real time monitoring and evaluation of the inhibition effect of fucoxanthin against α-amylase activity by using QCM-A

The main symptoms of diabetes are hyperglycemia and insulin resistance. The inhibition of the starch digestion enzymes could effectively regulate starch digestion and glucose absorption, thereby slowing or treating the symptoms of postprandial hyperglycemia. Herein, we used fucoxanthin isolated from Undaria pinnatifida stems, as α-amylase inhibitor, and monitored the interactions of both biomolecules by using quartz crystal microbalance-admittance (QCM-A) instrument. All the processes of α-amylase hydrolysis of starch were also dynamically tracked by using amylose-immobilized QCM technology. In our work, we found that the kinetic parameter (k _off, k _on, and k _cat) values obtained by the QCM-A analysis were relatively consistent compared to the kinetic parameter values obtained by the conventional Michaelis-Menten analysis. For the inhibitory reactions, the results showed that fucoxanthin significantly reduced the activity of α-amylase in a dose-dependent manner. The QCM-A technology shown to be an excellent approach in obtaining comprehensive and accurate kinetic parameters, thereby providing real and accurate data for kinetic studies. It is helpful to clarify the mechanism of action of fucoxanthin on α-amylase, which further proved the potential of fucoxanthin to improve and treat postprandial hyperglycemia.

Interfacial Selective Study on the Gelation Behavior of Aqueous Methylcellulose Solution via a Quartz Crystal Microbalance

It is important to understand the interfacial structure and physical properties of a polymer material to improve its function. In this study, we used a quartz crystal microbalance (QCM) and neutron reflectivity (NR) measurements to evaluate the viscoelasticity and structure of an aqueous methylcellulose solution near the gold interface. The apparent shear modulus, which was calculated from the complex frequency, was used to assess gelation behavior. The apparent shear modulus determined via the QCM suggested high-frequency rheological properties that reflected the relaxation of skeletal stretching and rotational motion of polymer segments, as well as cooperative motion of the various functional groups. The gelation temperature was found to be lowered at the interface in comparison with that of the bulk. It is suggested that the QCM can evaluate the shear modulus accompanying the gelation near the interface. The interfacial segregation on the gold substrate caused by the surface free energy and long-range van der Waals interaction was observed from NR measurements.

Critical In-Plane Density of Polyelectrolyte Brush for the Ordered Hydrogen-Bonded Structure of Incorporated Water

A polymer electrolyte brush is a reasonable platform to confine water molecules within a nanoscopic area to study their role in the function of interacting media because of their adjustable nanospace and charge by changing the in-plane density and side chains of the brush. Here, we demonstrate how the in-plane spacing of cationic polymer brush chains, poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMTAC), affects the hydrogen bond configuration of incorporated water using soft X-ray emission spectroscopy. At the critical in-plane density σ = 0.30 chains/nm² of PMTAC, tetrahedrally coordinated water molecules started to melt into distorted or broken hydrogen-bonded configurations. Considering the charge on the quaternary ammonium cations, the electric field required to form a tetrahedrally coordinated hydrogen-bonded configuration was estimated as ∼500 kV cm^-1 and is effective up to ∼1 nm from the surface of the polymer chain. These findings are useful for designing specific interface properties and the resultant surface function of polyelectrolyte-based materials.

Molecular Understanding of Fouling Induction and Removal: Effect of the Interface Temperature on Milk Deposits

Molecular details concerning the induction phase of milk fouling on stainless steel at an elevated temperature range were established to better understand the effect of temperature on surface fouling during pasteurization. The liquid-solid interface that replicates an industrial heat exchanger (≤75°C), including four stages (preheating, heating, holding, and cooling), was investigated using both a quartz crystal microbalance (QCM-D) and a customized flow cell. We found that the milk fouling induction process is rate-limited by the synergistic effects of bulk reactions, mass transfer, and surface reactions, all of which are controlled by both liquid and surface temperatures. Surface milk foulant becomes more rigid and compact as it builds up. The presence of protein aggregates in the bulk fluid leads to a fast formation of surface deposit with a reduced Young's modulus. Foulant adhesion and cohesion strength was enhanced as both interfacial temperature and processing time increased, while removal force increased with an increasing deposit thickness. During cleaning, caustic swelling and removal showed semilinear correlations with surface temperature (T_S), where higher T_S reduced swelling and enhanced removal. Our findings evidence that adsorption kinetics, characteristics of the foulant, and the subsequent removal mechanism are greatly dependent on the temperature profile, of which the surface temperature is the most critical one.

Comparison of cultured cell attachment on a temperature-responsive polymer, poly-L-lysine, and collagen using modeling curves and a thermal-controlled quartz crystal microbalance

The characteristics of cultured cell attachment onto poly-L-lysine (PLL), collagen, and the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) were studied using a quartz crystal microbalance (QCM). A QCM with microscope cameras enclosed in a Peltier chamber was developed to enable QCM measurements and microphotographic imaging to be conducted in a temperature-controlled CO₂ incubator. Human hepatoma cell line HepG2 cells were cultured on the quartz crystals coated with PLL, collagen, and PNIPAM. Response curves of the resonant frequency of the quartz crystals during the cell attachment process were analyzed on the basis of the parameters of modeling curves fit to the experimentally obtained curves. Analysis of the fitting curves showed that the time constants of the first-lag response were 11 h for PLL, 16 h for collagen, and 38 h for PNIPAM and that the frequency change for the PNIPAM films was six times smaller than those for the PLL and collagen films. These findings were supported by photographic images showing wider cell spread on PLL and collagen than on PNIPAM. The response of cells on PNIPAM was measured during a thermal cycle from 37 to 20 °C to 37 °C. In the resonance frequency-resonance resistance (F-R) diagram, the slopes of ΔR/ΔF corresponding to the cell attachment process and those corresponding to the thermal cycling process differed; the positions in the F-R diagram also shifted to higher resonant frequencies after the thermal cycle. These results suggested that the mass effect decreased as a result of the weakening of the cell attachment strength by the thermal cycle because the molecular brushes of PNIPAM were disarranged.

Bio-inert Properties of TEG Modified Dendrimer Interface

The bioinert interfaces that prevent adhesion of proteins and cells are important for biomaterial applications. In order to design a bioinert interface, the immobilization of an appropriate functional group and the control of molecular density is required. Dendrimer was modified with triethylene glycol (TEG) to display a dense brush structure. TEG with different density and terminal groups were immobilized with a dendrimer template and thiol terminated molecules. The inhibitory effect on protein and bacteria binding was investigated. The physical property of the interface was measured by QCM-admittance to clarify the factor of the bioinert property.

Ultrasensitive Poly(boric acid) Hydrogel-Coated Quartz Crystal Microbalance Sensor by Using UV Pressing-Assisted Polymerization for Saliva Glucose Monitoring

Quartz crystal microbalance (QCM) has attracted extensive attention in the field of biological analysis and detection because of its high sensitivity, fast response, real-time measurement, good operability, and low-cost production. However, to detect the trace amounts of small molecules, such as low-concentration saliva glucose under physiological conditions, is still a major challenge. Herein, the surface of a QCM chip was coated with a poly(boric acid)-based hydrogel using UV pressing-assisted polymerization to obtain a simple device for glucose detection. The designed QCM sensor shows a record-low detection limit of glucose (3 mg/L at pH 7.5), which is ∼30 times lower than that of sensors fabricated by conventional surface initiation-spin coating. The outperformance of the poly(boric acid) hydrogel-coated QCM sensor is probably due to the uniform and compact microstructure, as well as the presence of sufficient glucose-binding sites resulting from the hydrogel coating generated by UV pressing-assisted polymerization. This method provides an important solution to detect the trace amounts of small organic molecules or ions and has the potential to push forward the practical applications of QCM sensors.

Optomechanical detection of vibration modes of a single bacterium

Low-frequency vibration modes of biological particles, such as proteins, viruses and bacteria, involve coherent collective vibrations at frequencies in the terahertz and gigahertz domains. These vibration modes carry information on their structure and mechanical properties, which are good indicators of their biological state. In this work, we harnessed a particular regime in the physics of coupled mechanical resonators to directly measure these low-frequency mechanical resonances of a single bacterium. We deposit the bacterium on the surface of an ultrahigh frequency optomechanical disk resonator in ambient conditions. The vibration modes of the disk and bacterium hybridize when their associated frequencies are similar. We developed a general theoretical framework to describe this coupling, which allows us to retrieve the eigenfrequencies and mechanical loss of the bacterium low-frequency vibration modes (quality factor). Additionally, we analysed the effect of hydration on these vibrational modes. This work demonstrates that ultrahigh frequency optomechanical resonators can be used for vibrational spectrometry with the unique capability to obtain information on single biological entities.

Brushes, Graft Copolymers, or Bottlebrushes? The Effect of Polymer Architecture on the Nanotribological Properties of Grafted-from Assemblies

Surface-grafted polyzwitterions (PZW) have gained a foothold in the design of synthetic materials that closely mimic the lubricious properties of articular joints in mammals. Besides their chemical composition, the architecture of PZW brushes strongly determines their morphological, nanomechanical, and nanotribological characteristics. This emerges while comparing the properties of linear poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) brushes with those displayed by graft copolymer and bottlebrush brushes, either featuring a low or a high content of PMPC side chains. Surface-initiated atom transfer radical polymerization (SI-ATRP) enabled the synthesis of different branched-brush architectures from multifunctional macroinitiators via multiple grafting steps, and allowed us to modulate their structure by tuning the polymerization conditions. At relatively low grafting densities (σ), long PMPC side segments extend at the interface of bottlebrush and graft copolymer brushes, providing both morphology and lubrication properties comparable to those shown by loosely grafted, linear PMPC brushes. When σ > 0.1 chains nm^-2 the effect of the branched-brush architecture on the nanotribological properties of the films became evident. Linear PMPC brushes showed the lowest friction among the studied brush structures, with a coefficient of friction (μ) that reached 1 × 10^-4, as measured by atomic force microscopy (AFM). Bottlebrush brushes showed comparatively higher friction, although the high content of hydrophilic PMPC side chains along their backbone substantially improved lubrication compared to that displayed by the more sparsely substituted graft copolymer brushes.

Gas sensors based on mass-sensitive transducers part 1: transducers and receptors-basic understanding

The scientific interest in gas sensors is continuously increasing because of their environmental, medical, industrial, and domestic applications. This has resulted in an increasing number of investigations being reported in the literature and communicated at conferences. The present review, organized in two parts, addresses the peculiarities of gas sensors based on mass-sensitive transducers, starting with their structure and functionality and progressing to implementation and specific use. In this first part of the review, we discuss the constructional peculiarities and operation regions and the physical and chemical processes governing the reception and transduction functions and the way in which they influence the sensor sensing parameters/features. Scientific outcomes and trends in research into gas sensors based on mass sensitive transducers are also considered.

Mixing Poly(ethylene glycol) and Poly(2-alkyl-2-oxazoline)s Enhances Hydration and Viscoelasticity of Polymer Brushes and Determines Their Nanotribological and Antifouling Properties

Poly(2-alkyl-2-oxazoline)s (PAOXAs) have progressively emerged as suitable alternatives for replacing poly(ethylene glycol) (PEG) in a variety of biomaterial-related applications, especially in the designing of polymer brush-based biointerfaces because of their stealth properties and chemical robustness. When equimolar mixtures of PEG and PAOXAs are assembled on surfaces to yield mixed polymer brushes, the interfacial physicochemical properties of the obtained films are significantly altered, in some cases, surpassing the biopassive and lubricious characteristics displayed by single-component PAOXA and PEG counterparts. With a combination of variable angle spectroscopic ellipsometry, quartz crystal microbalance with dissipation, and atomic force microscopy-based methods, we demonstrate that mixing of PEG brushes with equimolar amounts of PAOXA grafts determines an increment in film's hydration and viscoelasticity. In the case of mixtures of PEG and poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline), brushes displaying full inertness toward serum proteins and improved lubricity with respect to the corresponding single-component layers can be generated, while providing a multifunctional surface that substantially enlarges the applicability of the designed coatings.

Initial Cell Adhesion onto a Phospholipid Polymer Brush Surface Modified with a Terminal Cell Adhesion Peptide

Dynamic changes in the properties of adsorbed protein layers at material surfaces make it difficult to analyze a cell adhesion behavior. Adhesion is affected by the ligand molecules in the adsorbed protein layers on the material's surface. This study aimed to quantitatively analyze the initial cell adhesion onto a polymeric surface modified with immobilized cell adhesion molecules with a well-defined structure. Peptides containing an arginine-glycine-aspartic acid (RGD) sequence were introduced at almost all the termini of the grafted poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] chains using a click reaction at a highly protein-resistant poly(MPC) brush layer. Thus, the surface could bind to the cell membrane proteins only through the immobilized RGD. Furthermore, the degree of polymerization of the grafted poly(MPC) chains could control the hydrated poly(MPC) brush layer softness, as determined by measuring the dissipation energy loss using a quartz crystal microbalance. At the initial stage of cell adhesion, the density of cells adhering to the RGD-immobilized poly(MPC) brush layers did not depend on the poly(MPC) brush layer softness. However, spreading of the adherent cells was inhibited on the RGD-immobilized poly(MPC) brush layers with a higher softness. Hence, the results suggested that the layer softness did not affect the binding number between the RGD and cell membrane protein during initial cell adhesion; however, the intracellular signaling triggered by the RGD-receptor interaction was inhibited. The poly(MPC) brush surface carrying immobilized cell adhesion molecules has the potential to analyze precisely the effect of the properties of cell adhesion molecules on initial cell adhesion.

Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation

In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model ( Physica Scripta 1999, 59, 391-396) and a more realistic power-law model ( Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/λ _n, is in the range of 0.05-0.20, where d is the film thickness and λ _n is the wavelength of the mechanical shear wave at the n^th harmonic. We further provide a framework for estimating the physical properties of soft materials in the megahertz regime by using the physical behavior of polyelectrolyte complexes. This provides the user with an approximate range of allowable film thicknesses for accurate viscoelastic analysis with either model, thus enabling better use of the QCM-D in soft materials research.

Quartz Crystal Microbalance Electronic Interfacing Systems: A Review

Quartz Crystal Microbalance (QCM) sensors are actively being implemented in various fields due to their compatibility with different operating conditions in gaseous/liquid mediums for a wide range of measurements. This trend has been matched by the parallel advancement in tailored electronic interfacing systems for QCM sensors. That is, selecting the appropriate electronic circuit is vital for accurate sensor measurements. Many techniques were developed over time to cover the expanding measurement requirements (e.g., accommodating highly-damping environments). This paper presents a comprehensive review of the various existing QCM electronic interfacing systems. Namely, impedance-based analysis, oscillators (conventional and lock-in based techniques), exponential decay methods and the emerging phase-mass based characterization. The aforementioned methods are discussed in detail and qualitatively compared in terms of their performance for various applications. In addition, some theoretical improvements and recommendations are introduced for adequate systems implementation. Finally, specific design considerations of high-temperature microbalance systems (e.g., GaPO₄ crystals (GCM) and Langasite crystals (LCM)) are introduced, while assessing their overall system performance, stability and quality compared to conventional low-temperature applications.

Thermoresponsive poly(glycidyl ether) brushes on gold: Surface engineering parameters and their implication for cell sheet fabrication

Thermoresponsive polymer coatings, optimized for cell adhesion and thermally-triggered cell detachment, allow the fabrication of confluent cell sheets with intact extracellular matrix. However, rational design guidelines for such coatings are rare, since temperature-triggered cell adhesion and detachment from thermoresponsive surfaces are mechanistically not well understood. Herein, we investigated the impact of molecular weight (2, 9, 24kDa), grafting density (0.04-1.4 chains nm^-2), morphology, and roughness of well-characterized thermoresponsive poly(glycidyl ether) brushes on the cell response at 37 and 20°C. NIH 3T3 mouse fibroblasts served as a model cell line for adhesion, proliferation, and cell sheet detachment. The cell response was correlated with serum protein adsorption from cell culture medium containing 10% fetal bovine serum. Intact cell sheets could be harvested from all the studied poly(glycidyl ether) coated surfaces, irrespective of the molecular weight, provided that the morphology of the coating was homogenous and the surface was fully shielded by the hydrated brush. The degree of chain overlap was estimated by the ratio of twice the polymer's Flory radius in a theta solvent to its interchain distance, which should be located in the strongly overlapping brush regime (2 R_f/l>1.4). In contrast, dense PNIPAM (2.5kDa) control monolayers did not induce protein adsorption from cell culture medium at 37°C and, as a result, did not allow a significant cell adhesion. These structural design parameters of functional poly(glycidyl ether) coatings on gold will contribute to future engineering of these thermoresponsive coatings on more common, cell culture relevant substrates.

STATEMENT OF SIGNIFICANCE

Cell sheet engineering as a scaffold-free approach towards tissue engineering resembles a milestone in regenerative medicine. The fabrication of confluent cell sheets maintains the extracellular matrix of cells which serves as the physiological cell scaffold. Thermoresponsive poly(glycidyl ether)s are highly cell-compatible and brushes thereof promote cell adhesion and growth without modification with additional cell adhesive ligands. Thus, a direct correlation of temperature-dependent serum protein adsorption and cell response with surface design parameters such as grafting density and molecular weight became accessible. Hence, surface engineering parameters of well-defined poly(glycidyl ether) monolayers for reproducible cell sheet fabrication have been identified. These design guidelines may also prove beneficial in the development of other brush-like thermoresponsive coatings for cell sheet engineering.

Hofmeister Effect on PNIPAM in Bulk and at an Interface: Surface Partitioning of Weakly Hydrated Anions

The effect of sodium fluoride, sodium trichloroacetate, and sodium thiocyanate on the stability and conformation of poly(N-isopropylacrylamide), in bulk solution and at the gold-aqueous interface, is investigated by differential scanning calorimetry, dynamic light scattering, quartz crystal microbalance, and atomic force microscopy. The results indicate a surface partitioning of the weakly hydrated anions, i.e., thiocyanate and trichloroacetate, and the findings are discussed in terms of anion-induced electrostatic stabilization. Although attractive polymer-ion interactions are suggested for thiocyanate and trichloroacetate, a salting-out effect is found for sodium trichloroacetate. This apparent contradiction is explained by a combination of previously suggested mechanisms for the salting-out effect by weakly hydrated anions.

Serum Protein-Resistant Behavior of Multisite-Bound Poly(ethylene glycol) Chains on Iron Oxide Surfaces

Recent surveys have shown that the number of nanoparticle-based formulations actually used at a clinical level is significantly lower than that expected a decade ago. One reason for this is that the physicochemical properties of nanoparticles fall short for handling the complexity of biological environments and preventing nonspecific protein adsorption. In this study, we address the issue of the interactions of plasma proteins with polymer-coated surfaces. With this aim, we use a noncovalent grafting-to method to functionalize iron oxide sub-10 nm nanoparticles and iron oxide flat substrates and compare their protein responses. The functionalized copolymers consist of alternating poly(ethylene glycol) (PEG) chains and phosphonic acid grafted on the same backbone. Quartz crystal microbalance with dissipation was used to monitor polymer adsorption kinetics and evaluate the resistance to protein adsorption. On flat substrates, functionalized PEG copolymers adsorb and form a brush in moderate or highly stretched regimes, with densities between 0.15 and 1.5 nm-2. PEG layers using phosphonic acid as linkers exhibit excellent protein resistance. In contrast, layers prepared with carboxylic acid as the grafting agent exhibit mitigated protein responses and layer destructuration. The present study establishes a correlation between the long-term stability of PEG-coated particles in biofluids and the protein resistance of surfaces coated with the same polymers.

Poly(glycidyl ether)-Based Monolayers on Gold Surfaces: Control of Grafting Density and Chain Conformation by Grafting Procedure, Surface Anchor, and Molecular Weight

For a meaningful correlation of surface coatings with their respective biological response reproducible coating procedures, well-defined surface coatings, and thorough surface characterization with respect to layer thickness and grafting density are indispensable. The same applies to polymeric monolayer coatings which are intended to be used for, e.g., fundamental studies on the volume phase transition of surface end-tethered thermoresponsive polymer chains. Planar gold surfaces are frequently used as model substrates, since they allow a variety of straightforward surface characterization methods. Herein we present reproducible grafting-to procedures performed with thermoresponsive poly(glycidyl ether) copolymers composed of glycidyl methyl ether (GME) and ethyl glycidyl ether (EGE). The copolymers feature different molecular weights (2 kDa, 9 kDa, 24 kDa) and are equipped with varying sulfur-containing anchor groups in order to achieve adjustable grafting densities on gold surfaces and hence control the tethered polymers' chain conformation. We determined "wet" and "dry" thicknesses of these coatings by QCM-D and ellipsometry measurements and deduced anchor distances and degrees of chain overlap of the polymer chains assembled on gold. Grafting under cloud point conditions allowed for higher degrees of chain overlap compared to grafting from a good solvent like ethanol, independent of the used sulfur-containing anchor group for polymers with low (2 kDa) and medium (9 kDa) molecular weights. By contrast, the achieved grafting densities and thus chain overlaps of surface-tethered polymers with high (24 kDa) molecular weights were identical for both grafting methods. Monolayers prepared from an ethanolic solution of poly(glycidyl ether)s equipped with sterically demanding disulfide-containing anchors revealed the lowest degrees of chain overlap. The ratio of the radius of gyration to the anchor distance (2 R_g/l) of the latter coating was found to be lower than 1.4, indicating that the assembly was rather in the mushroom-like than in the brush regime. Polymer chains with thiol-containing anchors of different alkyl chain lengths (C₁₁SH vs C₄SH) formed assemblies with comparable degrees of chain overlap with 2 R_g/l values above 1.4 and are thus in the brush regime. Molecular weights influenced the achievable degree of chain overlap on the surface. Coatings prepared with the medium molecular weight polymer (9 kDa) resulted in the highest chain packing density. Control of grafting density and thus chain overlap in different regimes (brush vs mushroom) on planar gold substrates are attainable for monolayer coatings with poly(GME-ran-EGE) by adjusting the polymer's molecular weight and anchor group as well as the conditions for the grafting-to procedure.