Polystyrene Block Research Articles

Synthesis and Self-Assembly of Poly(4-acetoxystyrene) Cubosomes.

Polymer cubosomes (PCs) are a recent class of self-assembled nanostructures with great application potential due to their high porosity and surface area. Currently, most reported PCs consist of polystyrene block copolymers (BCPs), for which self-assembly parameters are rather well understood. Changing the block chemistry would be desirable to introduce more functionality; however, knowledge of adapting the self-assembly process to new chemistries remains limited. This work, reports on synthesizing poly(ethylene oxide)-block-poly(4-acetoxystyrene) and its copolymers with styrene, and provide conditions for their self-assembly into PCs with high yield and high inner order. It is shown that the polarity of the starting solvent toward the corona block allows tuning of the final morphology by controlling the corona volume and packing parameter.

SEPS functionalized PEG copolymer for improved toughness without obvious plasticization in epoxy resin

AbstractThe effects of grafting level of polyethylene glycol (PEG) grafted styrene ethylene propylene styrene (SEPS) on the intrinsic brittleness of epoxy thermosets were studied. The SEPS‐g‐PEG block copolymer (BCP) was synthesized by grafting various grafting degree of PEG (i.e., 10%, 20%, 30%, and 40%) on polystyrene (PS) blocks of SEPS following Williamson ether synthesis method. A total of 10 wt% of the BCP modifiers were dispersed in epoxy thermosets. PEG side chains were miscible in the epoxy which formed a uniform BCP dispersion within the epoxy thermoset matrix. As the degree of PEG grafting was increased, the BCP phase was absorbed in the epoxy matrix. This absorption occurred because the increase in PEG grafting provided more miscible PEG chains to bind the BCP and epoxy nanostructures together. The differential scanning calorimeter and dynamic mechanical thermal analysis analyses indicated that BCP toughened epoxy exhibited an improved glass transition temperature (Tg). At a 40% PEG grafting degree in the BCP, the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) increased up to 80% and 180%, respectively. This trend suggested that the energy associated with fractures could be absorbed through the deformation of the softer phases when a load was applied to them.

PH-responsive size- and charge-selective block copolymer membrane for the separation of small proteins

Blue-light-induced RAFT polymerization was utilized to synthesize poly(N,N-dimethylacrylamide)–block–polystyrene (PDMA–b–PS) diblock copolymers to obtain 40 g per batch for membrane fabrication. Using a combination of self-assembly and non-solvent induced phase separation (SNIPS), larger isoporous membranes (≈ 0.5 m · 0.3 m) were fabricated with pore diameters of ≈ 25 nm in the dry state and around 4 nm in the wet state. These membranes were post-modified with hydrochloric acid to impart negatively charged, pH-responsive poly(acrylic acid)–block–polystyrene (PAA–b–PS) membranes. While all proteins like cytochrome C, insulin, lysozyme, myoglobin, and ovalbumin were fully rejected by the pristine PDMA–b–PS membrane, the PAA–b–PS membrane demonstrated selective rejection based on protein size and charge, effectively rejecting the proteins with a hydrodynamic radius Rh ≥ 1.9 nm. The PAA–b–PS membrane showed a real selectivity of 4.1 for the positively charged protein cytochrome C compared to the similarly sized, but negatively charged insulin, as well as a real selectivity of 16.1 towards the negatively charged ovalbumin. This illustrates the size- and charge-selective characteristics of the PAA–b–PS membrane for protein separation.

Synthesis and Electron Transporting Properties of Diblock Copolymers Consisting of Polyfluorene and Polystyrene.

Poly(9,9-di-n-octylfluorene) (PFO) is a promising material for polymer light-emitting diodes (PLEDs) due to its advantageous properties. To enhance its electron transporting capabilities, diblock polymers were synthesized by attaching polystyrene (PSt) chains of varying lengths to one end of the PFO molecule. In a comparative study with PFO homopolymer, the diblock polymers maintained similar thermal properties, absorption spectra, and photoluminescent stability, while exhibiting slightly deeper lowest unoccupied molecular orbital (LUMO) levels and higher crystallinity. Notably, diblock polymers with shorter polystyrene blocks demonstrated higher electron mobility than the PFO homopolymer and diblock polymers with excessively long polystyrene blocks. These findings suggest that the optimal chain length of the polystyrene block is crucial for maximizing electron mobility, thus offering valuable insights for designing high-performance PLED materials.

Functionalization of rubbery domains in SBS triblock copolymers for anion exchange membrane applications with enhanced robustness

A series of anion exchange membranes (AEMs) based on hydrogenated poly (styrene-b-butadiene-b-styrene) (h-SBS) triblock copolymers were prepared via thiol-ene click reaction of the mid-block polybutadiene with 6-mercapto-1-hexanol, followed by hydrogenation of the remaining double bonds, direct bromination of the pendant alcohol group, and substitution of with trimethylamine (TMA). The thiol-ene click reaction provided a facile and effective control of degree of functionalization up to 50 mol% of total CC bonds in the polymer. Membrane properties of the TMA-functionalized h-SBS for AEM applications were investigated by measuring ion exchange capacity (IEC), water uptake, and ion conductivity. h-SBS-TMA-1.83 with 24% degree of functionalization of polybutadiene block exhibited an IEC of 1.83 mequiv./g and the highest hydroxide ion conductivity of 93 mS/cm at 80 °C. IEC and hydroxide ion conductivity of all h-SBS AEMs were preserved after treatment with aq. 1 M NaOH solution at 80 °C for 4 weeks, demonstrating good alkaline stability. The h-SBS AEMs with quaternary ammonium groups tethered to the rubbery polybutadiene block of SBS showed better mechanical properties, lower water uptake, less water swelling under humidified conditions, and higher and more stable hydroxide conductivity at 80 °C than the ones tethered to the rigid polystyrene block of hydrogenated SBS AEMs. These results suggest that ionic group functionalization at the rubbery block of SBS provides mechanically more robust AEMs and is better AEM material design than that of glassy block functionalized AEM.

Poly(lactic acid) block improves ambient-temperature ionic conductivity of pentablock copolymer electrolyte

A polystyrene-b-poly(lactic acid)-b-poly(ethylene oxide)-b-poly(lactic acid)-b-polystyrene pentablock copolymer electrolyte (PSLE) is successfully prepared by ring-opening polymerization (ROP) of DL-lactide (DL-LA) with poly(ethylene oxide) (PEO) followed by atom transfer radical polymerization (ATRP) with styrene. Poly(lactic acid) (PLA) block made by the polymerization of DL-LA can not only reduce the crystallinity of PEO, but also balance the coordination properties of Li+, while polystyrene (PS) block acts as a hard block to improve the mechanical properties of PSLE. Here, the obtained PSLE achieves high ionic conductivity (1.3 × 10−4 S cm−1) under ambient temperature and wide electrochemical stable window (4.2 V). In addition, the PSLE shows outstanding stability, allowing the Li/PSLE/Li cell to cycle stably for more than 600 h at 0.1 mA cm−2 without an increase in polarization voltage. And LiFePO4/PSLE/Li cell shows an initial discharge capacity of 159 mA h g−1 and keeps a capacity retention of 94.6 % after 200 cycles at 0.1C under ambient temperature. The LiNi0.6Co0.2Mn0.2O2/PSLE/Li cell also delivers good cycling performance. These results suggest that multiblock copolymer electrolyte is very promising material for the preparation of solid polymer electrolytes (SPEs) suitable for lithium metal batteries.

2-Aminoanthracene Crystallization in Its Compatible Polystyrene Block: RAFT Synthesis and Enhanced Charge Retention in Pentacene Transistor Gate Dielectrics

2-Aminoanthracene Crystallization in Its Compatible Polystyrene Block: RAFT Synthesis and Enhanced Charge Retention in Pentacene Transistor Gate Dielectrics

Synthesis of block copolymer with cis-1,4-polybutadiene and isotactic-rich polystyrene using α-diimine nickel catalysts.

A series of styrene-butadiene di-block copolymers with high cis-1,4 unit content (greater than 92%) polybutadiene (PB) and isotactic-rich polystyrene (PS) (mmmm > 65%) was synthesized using α-diimine nickel catalysts (Ni-diimine). Four different Ni-diimine catalysts were synthesized via a complexing reaction between nickel (II) naphthenate and laboratory-made α-diimine ligands L1, L2, L3 and L4, which have different steric volume structures. The results indicate that the Ni-diimine catalyst prepared using the L4 ligand with a higher steric volume can effectively initiate the block polymerization of butadiene and styrene, and the resulting polymer has distinguished cis-1,4 structure unit PB and high isotactic-selective PS block. Differential scanning calorimetry and electrochemical performance tests show that these block copolymers with cis-1,4-regulated and isotactic-selective polymerization have advantages in terms of high-temperature and low-temperature resistance as well as corrosion resistance. Therefore, these copolymers are expected to be widely used in some harsh industrial environments.

Microstructure development and mechanical performance of MWCNTs/GNPs filled SEBS with different block content

AbstractPolystyrene‐poly (ethylene‐butylene)‐polystyrene (SEBS) nanocomposites have been regarded as promising thermoplastic elastomers for several industries owing to their distinct molecular platforms and properties. However, extending their applications requires a thorough understanding of the microstructural changes that nanoparticles induce in SEBS chains. In this work, we used two types of SEBS varying in polystyrene (PS) hard block contents to study the relationship between the structural changes and viscoelastic/mechanical properties of SEBS hybrid nanocomposites containing different multi‐walled carbon nanotubes: graphene nanoplatelets ratios. According to the results, the viscoelastic responses were strongly influenced by the PS block content and nanoparticles ratio, which had an appreciable contribution to the nanoparticles' dispersion state. This was explained in terms of intensified microphase separation induced by the favorable interactions between the carbon‐based nanoparticles and PS blocks. It was also found that the samples containing higher hard block content demonstrated more significant mechanical performance and toughness, which were enhanced by the addition of nanoparticles such that the highest ultimate strength of 24.58 MPa was obtained for the S30C0.5G0.5 sample. Furthermore, some mechanisms, including molecular disentanglements, dissociation of inter/intra‐molecular interactions, the orientation of the rubbery polyethylene butylene chains, and PS microdomain rearrangement, were supposed to interpret the energy dissipation capability of SEBS nanocomposites.

Development of Cost-Effective Membranes for Redox-Flow Batteries

Developing long-duration energy storage (LDES) systems is key to promoting the penetration of intermittent energy storage, such as solar and wind into the electric grid. DOE’s Long Duration Storage Shot establishes a target to reduce the cost of grid-scale energy storage by 90% for systems with durations of >10 hours. Non-aqueous RFBs (non-aqueous RFB) using earth-abundant materials are promising to fulfill this target. A key bottleneck to keeping RFB from market penetration is the lack of high-performance and cost-effective membranes. Membranes represent the most critical component in non-aqueous RFB, and they are decisive to the cell stack performance and cost. For example, the ionic conductivity of the membrane determines the power density of the RFBs, while ion selectivity and solvent uptake govern non-aqueous RFB cycle life. Herein, we will present recent progress in our team on the membrane development for the non-aqueous flow batteries.The ionic conductivity - mechanical strength tradeoff is a long-standing challenge for all polymer electrolyte development. In a redox flow battery, solvent uptake promotes membrane ionic conductivity but decreases its storage modulus due to the increased polymer chain relaxation. Two strategies are found effective to alleviate such a tradeoff i) selective plasticization of the ion-conductive block such as poly(ethylene oxide) (PEO) in a polystyrene (PS)− PEO−PS block copolymer (SEO) electroconductivity by glyme-type of solvent, and ii) enhancement of the membrane mechanical strength by creating hydrogen and ionic bonds between the polymer matrix and the inorganic scaffold. Mitigating redox-active species crossover poses another challenge in membrane design. We show that the cation exchanged single ion conducting membrane can effectively decrease the crossover of the polysulfide species in a Na metal – polysulfide hybrid flow battery, which promotes the RFB capacity retention, Columbia efficiency, and cycle life benchmarked to a commercial porous membrane. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program led by Dr. Imre Gyuk, in the Office of Electricity.

Thin film and bulk morphology of PI-PS-PMMA miktoarm star terpolymers with both weakly and strongly segregated arm pairs

A series of three homologous ABC miktoarm star terpolymers having a polyisoprene (PI), a polystyrene (PS) and a poly(methyl methacrylate) (PMMA) arm, is synthesized by living anionic polymerization. While the volume fraction of the PI and the PS blocks are kept equal and constant, the volume fraction of the PMMA block is varied. The room temperature bulk structure is characterized using small-angle X-ray scattering and transmission electron microscopy, while the structure of thin films is investigated using scanning electron microscopy, atomic force microscopy and X-ray reflectometry. For both bulk and thin films, it is found that the sample with the lowest volume fraction of PMMA has a morphology distinctly different from the two samples with larger PMMA volume fraction. All data for both bulk and thin film samples are consistent with an alternating lamellar structure for the lowest PMMA volume fraction sample. The two higher PMMA volume fraction samples show standing rod structure, however the details of the packing in the PMMA matrix differ depending on sample thickness. Overall, a structure with PI domains screened from interacting with PMMA by a PS shell is seen for both samples. In bulk, core-shell cylinders pack hexagonally, while a 100 nm thin film of the sample with the largest volume fraction of PMMA shows a square-lattice packing. The structuring is driven by two factors: i) the strong segregation of the PI-PMMA arm pair together with the weak segregation of the two arm pairs with a PS block and ii) the geometrical constraints resulting from the star architecture. No wetting layers are observed for any of the thin film samples, neither at the air-polymner surface or at the polymer-substrate interface.

Environmental life cycle assessment and economic comparison of different roof systems

Recently, the negative environmental impacts of the construction industry have been of great concern. Since roofs are a major part of the building components, they may play a significant role in generating environmental pollution. One of the solutions to improve the environment in the construction industry is to attempt to achieve a roof system with minimal environmental impact. In the present work, the life cycle assessment (LCA) of one square meter of concrete joists and chromite joists roofs with various types of concrete, clay and polystyrene blocks, concrete slab, and Uboot concrete slab from cradle to the gate and processing technique using Simapro 9.1.1.7 software with the CML-IA baseline)2001) was studied. Also, the results of LCA obtained from the CML-IA baseline method were compared with the results achieved from GaBi software. The sensitivity analysis was performed to find materials with the greatest role in pollution generation. Furthermore, the economic evaluation of the roofs according to the price list for the building on Iran's Plan and Budget Organization (PBO) was carried out. The roof of the Concrete joist and polystyrene block has performed the most suitable on the roofs due to global warming, acidification, and eutrophication. The global warming, acidification, and eutrophication results using the CML-IA baseline (World 2000) method were slightly different from the BEES+ and the IPCC techniques results. Concrete joist with concrete block roof is the most economical roof among the different roofs. The comparison of LCA of eight roof systems with Simapro 9.1.1.7 and Gabi software is the first-time study, which may indicate one of the originalities of the work.

Study on rheological behavior of polystyrene‐polyisoprene‐polystyrene around viscous flow transformation: Effect of polystyrene block content and molecular weight

AbstractThe flow behavior of triblock copolymer polystyrene‐polyisoprene‐polystyrene (SIS) was different below and above the viscous flow transition temperature (Tf). The study investigated the relationship between molecular structure (molecular weight and polystyrene block content) and the macroscopic rheological properties of SIS melt around Tf via capillary rheometer. The results indicated that below the Tf, shear viscosity of SIS melt was controlled by the polystyrene (PS) block content. On the other hand, above the Tf, shear viscosity was controlled by molecular weight. The rheological phenomena were explained based on the state change of the PS domains below and above Tf. The effect of PS block content on the viscous flow activation energy (Eη) and pressure drop of SIS melt was also investigated.

Solid State Li Metal/LMO Batteries based on Ternary Triblock Copolymers and Ionic Binders

Triblock copolymers containing an ionophilic polymerized ionic liquid block, sandwiched between two ionophobic polystyrene blocks, were investigated as solid polymer electrolytes (SPE) to simultaneously provide mechanically robust, free-standing membranes with high lithium conductivity and an optimized electrolyte composition. The conductivity reached 8 × 10–5 S cm–1 and 6.5 × 10–4 S cm–1 at 30 and 80 °C, respectively, with an anodic stability above 4.5 V. Highly stable Li metal symmetric cycling was demonstrated, with an overpotential of 130 mV for over 300 h at 50 °C at a current density of 0.5 mA cm–2/0.5 mAh cm–2. Attempts were also made to incorporate the SPE as the binder in an LMO cathode formulation. The best cell performance, however, was obtained when substituting the SPE in the LMO cathode formulation with a PMA solid-state gel electrolyte, resulting in a high-performance solid-state Li|polymer eletrolyte|LMO device with stable cycling at C/5, and an impressive capacity retention (i.e., 105 mAh g–1 after 150 cycles at 0.1 mA cm–2) with a Coulombic efficiency around 99.4%.

Evaluation of the Performance of Expanded Polystyrene Block on the Reduction of the Deck Cracking in Wide Integral Abutment Bridge

Longitudinal joints are thought to provide relief from expansion and contraction of the bridge deck owing to temperature change, shrinkage, and live loads, especially for a wide bridge. Historically, however, these joints have been known to leak, allowing chloride-laden water to reach the bottom of the deck overhang and even the exterior girders. Research conducted by Phares et al. indicated that the development of cracking in bridge decks seems less dependent on the total width of the deck and more so on internal restraint of the abutment to temperature changes and, in particular, gradients. Based on the finite element method (FEM) results, an effective solution to reduce cracking in the deck might be to place an isolation pad between the soil and the back side of the abutment. The primary objective of this paper is to investigate the effectiveness of an isolation foam block at the back of an integral abutment in reducing the stress-induced strain and the deck end longitudinal and diagonal cracking near the end of the deck with an integral abutment. To achieve this objective, a highway bridge (Viking Road Bridge) in Iowa, US, designed with a width of 228 ft, was selected for the study. The bridge deck has no longitudinal joints but, based on the previous research results, it was equipped with thermal isolation pads behind the abutment. The newly constructed bridge was monitored for over two years, and this was followed by multiple bridge inspections. An analytical study was conducted to investigate the efficiency of the isolation foam on the bridge deck end structural behavior. The results indicated that the thermal isolation foam is effective in reducing the temperature gradient through the abutment thickness, especially on extremely cold days. By reducing the temperature difference between the abutment and the deck, a thermal isolation block is effective at reducing the deck end strain and resisting deck end cracking. The FEM results indicated that the maximum deck stress-induced strain was 46% greater without the effects of the thermal isolation block and greater than the concrete cracking strain. This indicated that, without the thermal isolation pad, the Viking Road Bridge could crack at the end of its deck.

Cationic Half-Sandwich Tetrahydrofluorenyl Rare-Earth Metal Complexes as Stable Single-Site Catalysts for (Co)Polymerization of Styrene and Butadiene.

As indenyl-derivates, the tetrahydrofluorenyl ligands had an expanded "wingspan" with considerable steric hindrance. In this text, the rare-earth metal complexes bearing tetrahydrofluorenyl ligands have been synthesized and fully characterized by NMR (1H and 13C) and X-ray diffraction analyses. Upon the activation by [Ph3C][B(C6F5)4], all the scandium complexes exhibited excellent catalytic activity for highly syndioselective polymerization of styrene with a narrow molecular weight distribution (Mw/Mn < 2.0), suggesting the beneficial influence of tetrahydrofluorenyl ligands in stabilizing the single-site active species during the polymerization. Moreover, the scandium-based catalytic systems also promoted the 1,4-regular polymerization of butadiene and its copolymerization with styrene, affording diblock copolymers featuring a highly syndiotactic polystyrene block and a 1,4-specific PBD block. The kinetics investigation revealed the huge gap in TMS-Sc-catalyzed polymerization reactivity ratios (rBD/rSt > 300) between butadiene and styrene, and this further proved the block structure of styrene-butadiene copolymers. The morphology and mechanical property of the selected diblock copolymer were, respectively, investigated by atomic force microscopy and stress-strain experiments.

Dielectric properties OF 40SiO2–40P2O5–20ZrO2 /sulfonated styrene-ethylene-butylene-styrene hybrid membranes for proton exchange membrane fuel cells

The dielectric spectra of a series of hybrid membranes prepared with sulfonated styrene-ethylene-butylene-styrene (sSEBS) as the polymeric matrix, and zirconia-modified phosphosilicate (40SiO2–40P2O5–20ZrO2), as inorganic filler through direct infiltration, was analysed. All the membranes displayed characteristic sSEBS spectra, consisting of three molecular relaxations: A non-cooperative (β) relaxation and two cooperatives (αEB, αPS) ones ascribed to the glass transition of the ethylene-butylene and the polystyrene blocks, respectively. As a result of the infiltration of the inorganic component (40SiO2–40P2O5–20ZrO2), the dielectric spectra were considerably modified. Accordingly, the formation of dynamic crosslinking (M-O-M′ bonds, with M = P, Si, Zr) difficulties the motion of the αEB process, thus shifting it towards higher temperatures. Moreover, a significant plasticisation effect was found at high temperatures, which facilitates the activation of the αPS process. Furthermore, the decreasing values of the fragility parameter, due to the infiltration of the inorganic filler, revealed that all hybrid membranes displayed an arrangement of molecular chains and a strong behaviour. Thus, higher resistance to sudden temperature changes is expected. The optimum infiltration time (τinf) is between 10 and 20 min since it provides acceptable values of electric permittivity, and the induced dynamic crosslinking brings the glass transitions of both blocks closer. Consequently, a complete characterisation of the molecular mobility by studying the spectrum of dielectric relaxations enables to fine-tune the membranes for an optimum design focused on its application in a proton exchange membrane fuel cell (PEMFC).

Synthesis of Block Copolymers Containing Stereoregular Pendant Electroactive Blocks

The stereoregular nonconjugated pendant electroactive polymer (NCPEP) poly((N-carbazolylethylthio) propyl methacrylate) (PCzETPMA) has recently shown charge carrier mobilities that are on par with conjugated polymers. Here, we increased the complexity of the architecture for this NCPEP by introducing a polystyrene (PS) block via an anionic, living polymerization yielding a family of PS-b-PCzETPMA block copolymers as the first examples of NCPEP-block-copolymers with controlled stereoregularity of the NCPEP-blocks. Through this methodology we were able to control the molar masses, PS to PCzETPMA block ratios, and tacticities of the PCzETPMA-blocks. We found all three parameters to significantly impact the hole mobilities (μh) of the resulting copolymers, which increased with higher molar masses, longer PCzETPMA-blocks, and higher isotacticity of the PCzETPMA-block, giving the best μh of 2.33 × 10-5 cm2/V·s after annealing at 150 °C for the highest molar mass copolymer with a dominant isotactic PCzETPMA-block. This work is the first reported synthesis of a block copolymer bearing a NCPEP-block with a controlled tacticity and demonstrates that such complex polymer architectures can be realized with NCPEPs while maintaining control over their stereoregularity and without significantly suppressing the hole mobility in the resulting copolymers.

Soft, malleable double diamond twin

A twin boundary (TB) is a common low energy planar defect in crystals including those with the atomic diamond structure (C, Si, Ge, etc.). We study twins in a self-assembled soft matter block copolymer (BCP) supramolecular crystal having the double diamond (DD) structure, consisting of two translationally shifted, interpenetrating diamond networks of the minority polydimethyl siloxane block embedded in a polystyrene block matrix. The coherent, low energy, mirror-symmetric double tubular network twin has one minority block network with its nodes offset from the (222) TB plane, while nodes of the second network lie in the plane of the boundary. The offset network, although at a scale about a factor of 103 larger, has precisely the same geometry and symmetry as a (111) twin in atomic single diamond where the tetrahedral units spanning the TB retain nearly the same strut (bond) lengths and strut (bond) angles as in the normal unit cell. In DD, the second network undergoes a dramatic restructuring-the tetrahedral nodes transform into two new types of mirror-symmetric nodes (pentahedral and trihedral) which alternate and link to form a hexagonal mesh in the plane of the TB. The collective reorganization of the supramolecular packing highlights the hierarchical structure of ordered BCP phases and emphasizes the remarkable malleability of soft matter.

In-depth defect inspection of precast double walls using non-destructive techniques

Precast double walls are frequently used for building applications and consist of a pair of precast reinforced concrete shells connected by a lattice girder creating an inner cavity. Once placed at its final position this cavity is filled with freshly cast and compacted concrete. Aside from benefits such as increased ease in installation, reduced cost and shorter construction time also some pitfalls are recognized. Due to the restrained space and the presence of the truss girder undesired defects (e.g. voids, honeycombing, etc.) might occur without being noticed, as the outer wall elements also act as formwork. This actually might reduce the load capacity and jeopardize the structural integrity of the concrete structure. Therefore, different non-destructive tests are being used in order to assess the filling degree of the cavity in the double walls and to localize defects, with varying success ratio (i.e. the detectability). Different techniques were applied on a test wall with intentionally embedded defects (polystyrene blocks) with varying diameter: rebound hammer, ultrasonic pulse velocity via direct transmission, ultrasonic shear-wave tomography, ground penetrating radar and active infrared thermography. The success and the limits of these techniques for in depth defect localization are being discussed in this paper. The effect of the selected detection method and the surface-on-depth ratio of the defect itself has an effect on its detectability.